Waveplate and optical circuit formed from mesogen-containing polymer

ABSTRACT

Waveplates formed of mesogen-containing polymers and planar lightwave circuits containing such waveplates. Polymers have sidechains containing mesogens such as biphenyl-containing groups. Polymers may have a glass transition temperature between 100 C. and 300 C., and polymers may be stretched in excess of 150% to increase birefringence of polymer and provide thin films. Waveplates formed of stretched polymer films may have high biaxial birefringence.

[0001] This application claims benefit of U.S. Provisional ApplicationSerial No. 60/329,979, filed Oct. 16, 2001, the contents of which ishereby incorporated by reference into the present application for allpurposes as if fully put forth herein.

BACKGROUND OF THE INVENTION

[0002] Planar lightwave circuits (PLCs) in telecommunications, such asarrayed waveguide gratings (AWGs) used to multiplex or demultiplexmultiple optical signals transmitted over a single optical fiber,typically are formed of birefringent materials such as doped SiO₂ orLiNbO₃. Birefringence in planar waveguides complicates the design andoperation of PLCs. Planar waveguides as are found in AWGs typically havedifferent propagation constants for TE (transverse electric) and TM(transverse magnetic) waveguide modes caused by stress-inducedbirefringence introduced into the waveguides due to mismatchedcoefficients of thermal expansion of the substrate, core, and cladding.For AWGs, this difference in propagation constants produces a wavelengthshift between each AWG channel's peak response to the TE inputpolarization and that channel's response to the TM polarization. Thedifference between the wavelength of peak TE transmission and thewavelength of peak TM transmission is called a polarization dependentwavelength shift (PDW). Even a small PDW may be a concern because of theproblems it may cause, such as poor channel isolation as well asincreased polarization-dependent loss (PDL).

[0003] One way to compensate for birefringence is to formulate awaveplate of a rigid polyimide polymer having a heat resistance of 300°C. or higher, as disclosed in U.S. Pat. No. 6,115,514. The waveplatechanges the polarization state of light passing through the waveplate.The patent expresses a clear preference that the waveplate is formed ofa rigid polymer with no more than 2 rotatable chemical bonds. Theinterchain orientation and intermolecular interactions of the polymerbackbones creates birefringence and thermal stability as a sheet of thepolymer is uniaxially drawn or stretched. Further, the patent statesthat it is necessary for the polymer to have a heat resistance in excessof 300° C.

[0004] Another way to compensate for birefringence is to use abirefringent crystal waveplate. Reported in 1992, a quartz waveplate wasused to correct for polarization dependence in an arrayed-waveguidegrating (AWG) multiplexer, although the method had high loss. Morerecently, a thin (10 μm thick) LiNbO3 half waveplate created usingcrystal ion slicing was demonstrated that could substantially reduceloss. In this paper, concerns are expressed about the hygroscopic natureof polyimides and possible long-term changes due to environmentalfactors. In addition, the LiNbO3 work stated the desire to improvepolarization mode conversion ratios and the desire to create thinnerwaveplates for insertion loss reduction.

BRIEF SUMMARY OF THE INVENTION

[0005] The invention provides a polymeric waveplate and a planarlightwave circuit (PLC) containing the polymeric waveplate that correctsfor or introduces a desired amount of birefringence into the PLC,creating a desired effect on the polarization state of an optical signalpassing through the waveplate. The polymeric waveplate is formed of apolymer that has a mesogen in a side-chain of the polymer. The sidechainhas an optional linker that attaches the sidechain to the polymerbackbone and an optional spacer between the linker and the mesogen. Thewaveplate is formed by creating a thin film of the polymer and thenuniaxially drawing (stretching) it at an elevated temperature to createthe required degree of birefringence for the waveplate.

[0006] Birefringence in polymers can be created by inducing directionalstress/strain in a film. When this directional stress/strain is appliedto a polymer film, interchain orientation can result. The degree oforientation per unit stress/strain, and thus the magnitude of theinduced birefringence, differs for polymers of differing compositions.The rate at which this orientation develops is increased when thepolymer film is above its glass transition temperature. As thetemperature of the film becomes lower than the glass transitiontemperature, some degree of orientation, and thus some level ofincreased birefringence, can be maintained. The degree of orientationthat is maintained is influenced by the ability of the material todevelop intermolecular, interchain interactions above Tg which persistsas the temperature of the material falls below the glass transition.

[0007] One way to achieve such interactions is through stronginteractions between polymer backbones. Polyimides are a class ofmaterials that exhibits a degree of intermolecular, interchaininteraction, which results in superior mechanical and high temperatureproperties. This high degree of interaction also results inbirefringence in stressed polyimide films. In general, the higher thedegree of rigidity of the polyimide backbone, the higher the degree ofinterchain interaction and the lower the achievable elongation upondrawing. In fact, crystallinity has been observed in the most rigidmaterials. Species such as flexible groups in the backbone and flexiblesidechains ordinarily disrupt the degree of organization that thematerial can achieve. The presence of these moieties is thus ordinarilydeleterious to the degree of birefringence that can be developed. Theseobservations have been reported in the '514 patent, which expresses astrong preference for materials that contain no more than two (2)rotatable (swivel) bonds and thus a minimum degree of flexibility in thebackbone. Ordinarily, high-rigidity polyimides such as those in the '514patent exhibit high modulus and high glass-transition temperature Tg,and are not readily drawable to a significant degree. Stress musttherefore be developed in a precursor polyamic acid film by drawing orby constraining the film and relying on shrinkage stress or anisotropicsubstrate expansion to provide and/or maintain orientation. The moreflexible polymer precursor may then be further reacted, possibly underconstraint, to preserve orientation.

[0008] It appears that one of the problems associated with waveplatesformed of a high-rigidity polyimide is that the waveplate may beslightly warped rather than completely flat due to stresses introducedwhen forming the polymer into a waveplate. A waveplate formed of ahigh-rigidity polyimide can be warped to an extent that a surface of thewaveplate stands as much as 1 mm off of a flat, horizontal surface uponwhich the waveplate is laid, despite the waveplate being onlyapproximately 25 μm thick.

[0009] The polymers of this invention contain mesogenic side chains andare often composed of a more flexible backbone than the '514 patentteaches are possible if one desires to produce waveplate, and inparticular, half waveplate articles. Further, the polymers of thisinvention can be drawn at significantly lower processing temperaturesdue to the flexibility of the backbone and the presence of thesidechains. Although the flexibility of the backbone and presence ofside chains reduce interchain interactions from the polymer backboneitself, the mesogens associate with one another to provide the necessaryadditional degree of interaction that maintains the order created by thestretching process and enable high birefringence to be attained. Thusthe birefringence achieved during stress/strain above Tg provides a filmthat is suitable for use as a waveplate article after cooling andrelease from a stretching apparatus. This is achievable in spite of thepresence of more flexible bonds than the '514 patent suggests arepossible and in spite of the presence of side chains that wouldordinarily be regarded as deleterious to the development of interchaininteractions and thus to the development of sufficient birefringence forthe production of thin waveplate articles. The temperature stability ofthe waveplates produced using exemplary mesogenic polymers of thisinvention is suitable for use up to 145 C. and reliable performance hasbeen observed after repeated use at elevated temperature.

[0010] The incorporation of mesogenic structures as sidechains is ageneral concept that can, in principle, be applied to a variety ofbackbone structures and releases the technology from a reliance on“rigid” backbone materials as defined in the '514 patent. They can beused to create high-birefringence films from highly drawable, flexiblebackbones that are less prone to crystallinity and would otherwise beunlikely to be capable of high birefringence. Although the mesogenitself may in many embodiments of the invention not appreciablycontribute directly to the birefringence, its main purpose in theseembodiments is to simultaneously aid in the ability to draw (stretch)the polymer at temperatures well below 300° C. and raise the stabilityof the stretched structure through intermolecular interactions. Theability to strain the material over a wider range allows the productionof birefringent articles of varying and potentially continuous waveplateperformance. In addition, the mesogens help to provide low watersensitivity to the polymer when appropriately chosen.

[0011] The polymer may be uniaxially or biaxially drawn, and ispreferably uniaxially drawn to create the birefringence necessary for awaveplate. An exemplary 15 μm thick half waveplate for operation at 1550nm wavelength requires a birefringence of 0.52. The polymer of theinvention can be cast into a thin film of appropriate thickness greaterthan 15 μm, and drawn to achieve the desired 15 μm thickness and 0.052birefringence. Alternatively, the thickness of the cast film can bechosen such that the film can be drawn to a higher level ofbirefringence to facilitate a half waveplate as thin as 8 μm for thesame application.

[0012] When forming a waveplate, the drawability, or ease with which thepolymer can be drawn, is advantageously good, as evidenced by the largeextent to which the polymer may be drawn. For instance, the polymer maybe uniaxially drawn with elongation (localized change in length dividedby original length) in excess of 50%, and is often drawn with elongationon the order of 100%-200%.

[0013] A waveplate of the invention preferably has a warpage of lessthan about 350 μm, more preferably less than about 250 μm warpage, andmore preferably still less than about 150 μm warpage. Warpage ismeasured by placing the waveplate on a flat, horizontal surface andmeasuring the distance from that surface to the highest point on theresting waveplate.

[0014] What is disclosed by way of example and not by way of limitationis:

[0015] A waveplate comprising a mesogen-containing polymer film having abackbone and having sidechains containing mesogen groups, wherein themesogen-containing polymer film has a length, a width, and a thicknesssuch that said mesogen-containing polymer film is insertable into achannel in an optical pathway of the planar lightwave circuit.

[0016] A waveplate according to paragraph [0014] wherein saidmesogen-containing polymer film has a birefringence sufficiently high torotate or convert a polarization state of an optical signal traversingthe optical pathway.

[0017] A waveplate according to paragraph [0015] wherein thebirefringence is at least 0.52.

[0018] A waveplate according to paragraph [0015] wherein the waveplateis a half waveplate of thickness between 5 and 25 μm.

[0019] A waveplate according to paragraph [0015] wherein the waveplateis a quarter waveplate of thickness between 5 and 25 μm.

[0020] A waveplate according to paragraph [0014] wherein themesogen-containing polymer film is formed of a polymer having a glasstransition temperature between 100 C. and 300 C.

[0021] A waveplate according to paragraph [0014] wherein the backbonecontains monomers having at least two groups that provide rotationalfreedom within the backbone.

[0022] A waveplate according to paragraph [0014] wherein the waveplatehas a warpage of less than 350 μm.

[0023] A waveplate according to paragraph [0014] wherein the backbonecomprises a polymer selected from the group consisting of: polyimides,polyetherimides, polyesterimides, polyamideimides, polyketones,polyarylethers, polyetherketones, polysulfones, polysulfides,polyarylenes, polyesters, polyamides, polycarbonates, polyolefins,polyvinylesters, polyurethanes, polyacrylates, polyphenylenes.

[0024] A waveplate according to paragraph [0022] wherein the backbonecomprises polyetherimide polymer.

[0025] A waveplate according to paragraph [0022] wherein the backbonecomprises polyamide polymer.

[0026] A waveplate according to paragraph [0023] wherein the backbone isformed of one or more components selected from the group consisting of4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride);4,4′-(hexafluoroisopropylidene) diphthalic anhydride;2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.

[0027] A waveplate according to paragraph [0024] wherein the backbone isformed of one or more components selected from the group consisting ofisophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).

[0028] A waveplate according to paragraph [0026] wherein the backbone isformed of isophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.

[0029] A waveplate according to paragraph [0026] wherein the backbone isformed of 2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).

[0030] A waveplate according to paragraph [0014] wherein the mesogengroups have the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X isselected from the group consisting of azo, diazo, azoxy, nitrone,carbon-carbon double bond, carbon-carbon triple bond, amide, imide,Schiff base, and ester; and R is selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.

[0031] A waveplate according to paragraph [0014] wherein the mesogengroups are selected from the group consisting of trans 1,3 cyclohexane;trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

[0032] A waveplate according to paragraph [0022] wherein the mesogengroups have the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X isselected from the group consisting of azo, diazo, azoxy, nitrone,carbon-carbon double bond, carbon-carbon triple bond, amide, imide,Schiff base, and ester; and R is selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.

[0033] A waveplate according to paragraph [0022] wherein the mesogengroups are selected from the group consisting of trans 1,3 cyclohexane;trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

[0034] A waveplate according to paragraph [0014], [0022], [0023], or[0024] wherein the mesogen group is biphenyl.

[0035] A waveplate according to paragraph [0014] wherein the mesogengroups comprise at least two aromatic groups and wherein the mesogengroups associate to help maintain birefringence as the film is drawn.

[0036] A waveplate according to paragraph [0014] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting of:ether, ester, amide, imide, urethane, alkylene, alkyl.

[0037] A waveplate according to paragraph [0022] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

[0038] A waveplate according to paragraph [0029] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

[0039] A waveplate according to paragraph [0030] wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting ofether, ester, amide, imide, urethane, alkylene, alkyl.

[0040] A waveplate according to any of paragraphs [0014], [0022],[0029], [0030], and [0034]-[0038] wherein the side chains furthercomprise spacing groups linking the mesogen groups to the linkinggroups, the spacing groups being selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.

[0041] A waveplate according to paragraph [0014] wherein the spacinggroups are sufficiently long and sufficiently flexible to allow themesogens of adjacent sidechains to associate as a film of themesogen-containing polymer is stretched.

[0042] A planar lightwave circuit comprising a waveguide and a waveplateaccording to any of paragraphs [0014]-[0040] positioned in an opticalpathway of the waveguide.

[0043] A planar lightwave circuit according to paragraph [0041] whereinthe waveplate is a half waveplate.

[0044] A planar lightwave circuit according to paragraph [0041] whereinthe waveplate is a quarter waveplate.

[0045] A planar lightwave circuit according to paragraph [0041] whereinthe waveplate resides in a channel cut or etched through the waveguide.

[0046] A planar lightwave circuit according to paragraph [0041] whereinthe waveguide is one of a plurality of waveguides of an arrayedwaveguide grating positioned between two free propagation regions of theplanar lightwave circuit, and wherein the waveplate is positioned in anoptical pathway of each of the plurality of waveguides of the arrayedwaveguide grating.

[0047] A planar lightwave circuit according to paragraph [0041] whereinthe waveguide is positioned at an angle to the waveguides that reducesback reflection caused by the waveplate groove, glue, and waveplate.

[0048] A method of making an optical device comprising

[0049] (a) providing a mesogen-containing polymer film; and

[0050] (b) forming the mesogen-containing polymer piece to have alength, a width, and a thickness adapted for use in a planar lightwavecircuit, the mesogen-containing polymer piece having a birefringence notequal to zero, said birefringence being suitable for use in a waveguideof a planar lightwave circuit

[0051] A method according to paragraph [0047] and further comprisinginserting the polymer piece into an optical pathway of a waveguide ofthe planar lightwave circuit.

[0052] A method according to paragraph [0047] wherein themesogen-containing polymer film has a polymer backbone selected from thegroup consisting of polyimides, polyetherimides, polyesterimides,polyamideimides, polyketones, polyarylethers, polyetherketones,polysulfones, polysulfides, polyarylenes, polyesters, polyamides,polycarbonates, polyolefins, polyvinylesters, polyurethanes,polyacrylates, polyphenylenes.

[0053] A method according to paragraph [0047] wherein themesogen-containing polymer film contains at least one mesogen having theform phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from thegroup consisting of azo, diazo, azoxy, nitrone, carbon-carbon doubleborid, carbon-carbon triple bond, amide, imide, Schiff base, and ester;and R is selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.

[0054] A method according to paragraph [0047] wherein the mesogen groupsare selected from the group consisting of trans 1,3 cyclohexane; trans1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

[0055] A method according to paragraph [0051] wherein themesogen-containing polymer film contains at least one mesogen having theform phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from thegroup consisting of azo, diazo, azoxy, nitrone, carbon-carbon doublebond, carbon-carbon triple bond, amide, imide, Schiff base, and ester;and R is selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.

[0056] A method according to paragraph [0051] wherein the mesogen groupsare selected from the group consisting of trans 1,3 cyclohexane; trans1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.

[0057] A method according to paragraph [0047] wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0058] A method according to paragraph [0051] wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0059] A method according to paragraph [0052]wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0060] A method according to paragraph [0053] wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0061] A method according to paragraph [0054] wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0062] A method according to paragraph [0055] wherein themesogen-containing polymer film has at least one linking group selectedfrom the group consisting of ether, ester, amide, imide, urethane,alkylene, alkyl.

[0063] A method according to any of paragraphs [0047] and [0051]-[0061]wherein the mesogen-containing polymer film has at least one spacergroup selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.

[0064] A method of using a mesogen-containing polymer, said methodcomprising processing the mesogen-containing polymer into a film withbirefringence in the plane of the film, inserting the mesogen-containingpolymer film into an optical pathway of a waveguide of a planarlightwave circuit such that the polymer effects a change in an opticalsignal transmitted through the waveguide and the polymer.

[0065] A method of using a mesogen-containing polymer comprising passingan optical signal having a first polarization state through a waveguideand the polymer such that the optical signal has a second polarizationstate not identical to the first polarization state.

[0066] Among other factors, the invention is based in the technicalfinding that a preferred polymer formed of a flexible polymeric backbonehaving a mesogen attached to the backbone through a linker and a spacercan be drawn uniaxially to provide a thin preferred waveplate (typicallyless than 20 μm thick) that is flat and can be inserted into a planarlightwave circuit while the intermolecular interactions enhanced by themesogens maintain sufficiently high birefringence in the stretchingprocess to allow the waveplate to compensate for polarization effectscreated by birefringence elsewhere in the PLC. Such preferred polymer isdrawn in a single step at temperatures well below 300° C., and can bedrawn up to in excess of 150% to achieve high birefringence up to inexcess of 0.1 with a high degree of repeatability and uniformity. Themesogen helps maintain the birefringence created in drawing as long asthe waveplate is operated sufficiently below the Tg of the polymer. Themesogen of the preferred waveplate also acts much as an internalplasticizer acts, reducing the glass-transition temperature (Tg) so thatthe fully-reacted polymer can be reliably and repeatably drawn to formthe waveplate without need for further reacting of the polymer (such asimidization) during or after drawing, and without need for appreciablesolvent content in the film. These technical findings and advantages andothers are apparent from the discussion herein.

BRIEF DESCRIPTION OF THE FIGURES

[0067]FIG. 1 is a graph of birefringence as a function of the localelongation (localized change in length divided by original length) foran exemplary material.

[0068]FIG. 2 shows the thickness of a half waveplate and a quarterwaveplate made from the material of FIG. 1, as a function of the localelongation.

[0069]FIG. 3 is a graph of birefringence as a function of the localelongation (localized change in length divided by original length) foranother exemplary material.

[0070]FIG. 4 shows the thickness of a half waveplate and a quarterwaveplate made from the material of FIG. 3, as a function of the localelongation.

[0071]FIG. 5 is a graph of the calculated insertion loss due to awaveplate groove as a function of the groove width.

[0072]FIG. 6 depicts monomers used to form a mesogen-containingpolyetherimide polymer and the resultant polymer that can be used inoptical devices of the invention.

[0073]FIG. 7 depicts monomers used to form a mesogen-containingpolyamide polymer and the resultant polymer that can be used in opticaldevices of the invention.

[0074]FIG. 8 illustrates a PLC of the invention, an arrayed waveguidegrating.

[0075]FIG. 9 illustrates another PLC of the invention, a wavelengthdivision multiplexer based on a Mach-Zehnder interferometer.

[0076]FIG. 10 depicts a set of reactions to form a monomer used informing the polymer depicted in FIG. 6.

[0077]FIG. 11 depicts an additional set of reactions to form anothermonomer used in forming the polymer depicted in FIG. 7.

[0078]FIG. 12 depicts monomers used to form a mesogen-containingpolyamide polymer and the resultant polymer that may be useful inoptical devices of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0079] A waveplate of the invention formed of a mesogen-containingpolymer is useful in compensating for birefringence in a planarlightwave circuit (PLC). A PLC typically is formed of a birefringentmaterial such as doped silicon oxide or lithium niobate, such that thetransverse electric (TE) and transverse magnetic (TM) modes of theoptical signal travel at different velocities through the material andarrive at a given part of the PLC or a detector integrated into the PLCout of phase. In many instances, a thin half waveplate inserted into theoptical path of the PLC with its principle axis oriented at 45° to theplane of the PLC compensates for problems generated by birefringence inany part of the PLC. Thus, the TE and TM modes arrive at the desiredpart of the PLC within a period of time of each other that allows thePLC to function independently of input polarization without having toitself compensate for the birefringence.

[0080] In practical PLC devices made from practical PLC materials suchas doped silicon oxide, polymers, silicon oxide and polymers, or lithiumniobate, TE and TM modes of an optical signal can also experiencediffering loss of intensity through the components of a PLC device suchas waveguides, couplers, star couplers, and waveguide gratings. Thisloss difference is called polarization dependent loss (PDL), and ispreferably minimized, most preferably zero, although in practical PLCdevices, the PDL can be unacceptably large. In many instances, a thinhalf waveplate inserted into the optical path of the PLC with itsprinciple axis oriented at 45° to the plane of the PLC compensates forPDL by causing equivalent losses for light entering the waveguide in TEand TM modes.

[0081] Cutting a groove in a PLC and inserting the waveplate in the PLCcauses undesirable additional loss, termed insertion loss, of the lightin the PLC. The loss occurs when light in a waveguide reaches the grooveand waveplate, and rapidly spreads by diffraction. When it reaches thewaveguide on the other side of the groove, not all the light can make itback into the single-mode waveguide. A groove made wider to accommodatea wider waveplate will have higher loss, thus a narrower groove (andthus narrower waveplate) are preferable. FIG. 5 shows the theoreticalinsertion loss caused by a waveplate groove as a function of the groovewidth. This additional insertion loss decreases with decreasing width ofthe groove into which the waveplate is inserted, which is typically 2-10μm wider than the thickness of the waveplate. Thus it is desirable tohave a waveplate of a minimal practical thickness to allow a groove ofminimum practical thickness which in turn gives the minimum practicalinsertion loss. For this reason, the waveplate is typically made quitethin, being less than 30 μm, preferably less than about 20 μm, and morepreferably less than 15 μm thick.

[0082] Further, as mentioned above, preferred waveplates of thisinvention have little warpage. A flat waveplate requires a thinnerchannel for insertion into a PLC than does a warped waveplate.Oftentimes it is extremely difficult to insert a warped waveplate,especially one made of a rigid polyimide, into a channel cut in a PLC tohave about the same thickness as the waveplate polymer. It sometimes canbe necessary to form a channel of greater width than would be formed fora flat waveplate to allow a warped waveplate to be inserted into thechannel within a reasonable period of time. A flat waveplate as providedin certain embodiments of this invention can therefore aid in reducinginsertion loss, since the channel in the PLC into which the waveplate isinserted can be formed only about 2-5 μm wider than the waveplatethickness.

[0083] Polymers typically have a much lower transmittance of opticalpower per unit thicknesss than waveguides made of inorganic materialssuch as SiO₂ or LiNbO₃ as found in many PLCs (especially those of theinvention). Consequently, thin polymeric waveplates made using amesogen-containing polymer often transmit more optical power than dothicker polymeric waveplates. Additionally, the use of mesogens allowsmore flexibility in selecting a polymer backbone with low opticalabsorption.

[0084] The most commonly used waveplates in PLC devices are quarter andhalf waveplates for use at the common optical communication wavelengthsof 1300 nm and 1550 nm. Examples of waveplates that may be used with PLCdevices include a 7.5 μm thick quarter waveplate at 1300 nm (requiring abirefringence of 0.043), a 7.5 μm thick quarter waveplate at 1550 nm(requiring a birefringence of 0.052), a 15 μm thick half waveplate at1550 nm (requiring a birefringence of 0.052), and a 10 μm half waveplateat 1550 nm (requiring a birefringence of 0.078). A polymer for use inmaking waveplates therefore is preferably capable of reaching orexceeding a birefringence when drawn of 0.043, more preferably 0.052,and even more preferably 0.078.

[0085] A mesogen-containing polymer is made into a waveplate by drawing(stretching) and heating a thin film of the polymer that starts withlittle or no in-plane birefringence. The birefringence of the polymerfilm used to make the waveplate may be achieved by stretching eitheruniaxially and/or biaxially by any method known to one of ordinaryskill. A mesogen-containing polymer often increases in birefringence asthe polymer is drawn. The mesogens align and associate during thedrawing process to maintain sufficient birefringence in the flexiblefilm to rotate polarization or convert from one form of polarization toanother (such as from linear to circular), for instance. An exemplarymesogen-containing polymer of this invention is presented later in whichthe maximum attained birefringence upon drawing is greater than 0.105.Such a polymer can be drawn less than this maximum amount to achieve thenecessary birefringence of 0.052 to make a 15 μm half waveplate for useat 1550 nm wavelength, for example.

[0086] Most often a ½ waveplate or a ¼ waveplate is used. However anyvalue between 0 and 1 or more waves is often obtainable with amesogen-containing polymer. For example, the waveplate may differ fromthese established values by a small amount to allow the waveplate to beinserted into a PLC at an angle slightly different from perpendicular tothe direction of light propagation such that the light in the waveguideexperiences the desired effect.

[0087] The waveplate may be a transmissive waveplate, in which anoptical signal exits a face opposite to the face of the waveplate thatthe signal entered. Alternatively, the waveplate may be a reflectivewaveplate, in which one face of the waveplate is coated with areflective substance such as gold, sliver, aluminum, copper, palladium,nickel, or titanium by sputter-coating a stretched polymer film prior toforming the waveplate. The reflective coating reflects an optical signalback through the polymer film through which it traveled to reach thecoating, allowing the polymer film to be only half as thick as wouldotherwise be needed to effect a desired change in an optical signal.

[0088] The polymer used to form the waveplate has a mesogen attached toa polymeric backbone by a linker and an optional spacer. This generalconfiguration is also found in side chain polymer liquid crystals, andmany polymers suitable to form side chain polymer liquid crystals can beused as the basis to form waveplates and PLCs of the invention byforming the polymer to have a suitable molecular weight and by reducingthe number of mesogen groups present on a polymer molecule so that thepolymer does not form large liquid crystal phases that would otherwisediffract or block light from passing through the polymer.

[0089] Each of the components of the polymer is discussed in turn.

[0090] Mesogen

[0091] As a film of mesogen-containing polymer is drawn, the mesogensassociate to maintain the birefringence after the film is drawn. Themesogen may be any single or combination of mesogens used in makingliquid crystal polymers. Thus, usually the mesogen is made up of a rigidcore of one or multiple aromatic rings.

[0092] A mesogen as used in the waveplate or PLC of the invention may bea compound as depicted in Formula 1 and/or Formula 2:

-phenyl-phenyl-R  Formula 1

-phenyl-X-phenyl-R  Formula 2

[0093] where X is any rigid central linkage that keeps one phenyl groupin a fixed spatial relationship with the other phenyl group to which itis attached, including azo, diazo, nitrone, azoxy, carbon-carbon doublebond (to give stilbene), carbon-carbon triple bond (to give tolan),amide, imide, Schiff base, and ester; and R is a substituent such ashydrogen or a flexible spacer such as an alkyl, cycloalkyl, aryl,aralkyl, alkaryl, cyano, alkoxy, acyloxy, or halogen. Examples of thesegroups are listed in Table 1.

[0094] Preferred mesogens include:

[0095] phenyl-phenyl (R is hydrogen)

[0096] phenyl-phenyl-cyano

[0097] phenyl-phenyl-acyloxy

[0098] phenyl-phenyl-alkyl (length 1-18 carbons)

[0099] phenyl-phenyl-aryl

[0100] phenyl-C double bond C-phenyl (R is hydrogen)

[0101] phenyl-C double bond C-phenyl-cyano

[0102] phenyl-C double bond C-phenyl-acyloxy

[0103] phenyl-C double bond C-phenyl-alkyl (length 1-18 carbons)

[0104] phenyl-C double bond C-phenyl-aryl

[0105] phenyl-C triple bond C-phenyl (R is hydrogen)

[0106] phenyl-C triple bond C-phenyl-cyano

[0107] phenyl-C triple bond C-phenyl-acyloxy

[0108] phenyl-C triple bond C-phenyl-alkyl (length 1-18 carbons)

[0109] phenyl-C triple bond C-phenyl-aryl

[0110] phenyl-ester-phenyl (R is hydrogen)

[0111] phenyl-ester-phenyl-cyano

[0112] phenyl-ester-phenyl-acyloxy

[0113] phenyl-ester-phenyl-alkyl (length 1-18 carbons)

[0114] phenyl-ester-phenyl-aryl

[0115] phenyl-amide-phenyl (R is hydrogen)

[0116] phenyl-amide-phenyl-cyano

[0117] phenyl-amide-phenyl-acyloxy

[0118] phenyl-amide-phenyl-alkyl (length 1-18 carbons)

[0119] phenyl-amide-phenyl-aryl

[0120] phenyl-azo-phenyl (R is hydrogen)

[0121] phenyl-azo-phenyl-cyano

[0122] phenyl-azo-phenyl-acyloxy

[0123] phenyl-azo-phenyl-alkyl (length 1-18 carbons)

[0124] phenyl-azo-phenyl-aryl

[0125] In addition to the forms specified by Formula 1 and Formula 2above, mesogens may include other ring structures that associate withone another with an affinity similar to the structures above, such astrans 1,3 cyclohexane; trans 1,4 cyclohexane; trans 2,5 disubstituted1,3 dioxane; trans 2,5 disubstituted 1,3 dithiane; and trans 2,5disubstituted 1,3 dioxathiane.

[0126] In a liquid crystal polymer, the mesogens attached to the polymerbackbone are found in one layer, and the polymer backbones localize inanother layer characteristic of the smectic phase. This may in certaininstances help to form a double-comb structure where side chains pointaway from the backbone in an alternating manner.

[0127] In a polymer of the invention, it is believed that no appreciablesmectic phase is formed, although birefringence does increase as apolymer film is stretched. It is believed that some mesogens on polymerbackbones may align with one another, but the extent to which suchalignment occurs is either insufficient to form separate phases in thepolymer or, if separate phases form, the extent to which the separatephases are present is not so great that the optical signal is scatteredor lost to the extent that occurs in liquid crystal polymers. Themesogen is present in an amount sufficient to maintain a desiredbirefringence in the waveplate as the polymer is stretched to form afilm of a thickness suitable to form the waveplate.

[0128] The polymer has a sufficient number of mesogen groups present init to provide a birefringent film that can be formed into a waveplate bydrawing at reasonable temperature as described herein. The polymer mayhave a single mesogen or multiple mesogens per repeating unit of thepolymer, although generally the polymer has fewer than one mesogen perrepeating unit on average. Generally, from about 5 to about 75% of themonomers (mole/mole) have a mesogen attached, preferably from about 10to about 50% of the monomers have a mesogen attached to them. In anexemplary polymer of this invention, two mesogens are attached to one ofevery five repeat units of the backbone.

[0129] The mesogen-containing polymer may be a random polymer, in whichcase mesogen groups are distributed randomly along the polymer.Alternatively, the mesogen-containing polymer may be a block copolymerhaving mesogen groups deliberately clustered together in one or moresegment(s) of the polymer chain.

[0130] Polymer Backbone

[0131] The polymeric backbone may be a linear polymer such as a polymerformed of one or more of the following monomers or repeating units:olefin, etherimide, ester, vinyl ester, urethane, amide, imide, amideimide, ester imide, acrylate, etherketone, aryl ether, carbonate,sulfone, and phenylene. The linear chains of the polymer backbone mayslide past one another to some degree to allow the polymer to bestretched along one or more axes. The mesogens also promote slippage ofpolymer chains past one another, since the mesogens and their optionalspacers help to separate polymer chains and may reduce substantialentanglements that would otherwise limit stretching. Backbone polymersmay be chosen to provide the desired degree of thermal stability.Preferable backbone polymers include polyimides, polyetherimides,polyesterimides, polyamideimides, polyketones, polyarylethers,polyetherketones, polysulfones, aromatic polysulfides, polyarylenes,aromatic polyesters, aromatic polyamides, and aromatic polycarbonates.

[0132] Polymers used to form the waveplate preferably have at least twoswivel bonds per repeat unit incorporated into the backbone that allowportions of the backbone to rotate relative to one another. The polymercan be made flexible and can be drawn to a large extent due at least inpart to these groups. Such groups include single-bonded carbon,nitrogen, oxygen, sulfur, silicon, and other such groups well-known inthe art.

[0133] One particularly preferred backbone polymer is a polyetherimide.A polyetherimide is a flexible polymer because the ether linkages allowthe groups to which the ether linkage is attached to rotate or assumemany different positions. It is believed that a polyetherimide has adegree of movement in the backbone that permits the mesogens toassociate with one another to maintain birefringence, especially as afilm of the polymer is stretched.

[0134] Optional Linker

[0135] An attachment group, or linker, is any group that permits themesogen to be attached to the polymer backbone. A polymer formed of anacrylate or vinyl acetate attaches the mesogen to the hydrocarbonthrough the ester of the acrylate or acetate groups, respectively. Inthis instance, the ethylene unit of the vinyl acetate or acrylate willbe part of the backbone. The mesogen may be attached directly to thelinker, or the mesogen may be attached to a spacer that is itselfattached to the linker. Suitable linkers include ester, ether, imide,amide, urethane and saturated or unsaturated aliphatic groups asdescribed below for spacers. Preferred linkers include esters, ethers,amides and alkylenes.

[0136] Optional Spacer

[0137] The spacer is an optional group that allows the mesogens to movesomewhat independently of the polymer backbone. The spacer and linkertogether have a length that allows the mesogen to associate with anothermesogen attached to the same polymer backbone and/or to a differentpolymer backbone. Thus, mesogens may associate with one another despitepolymer chain entanglement or lack of polymer backbone orientation alongany one general direction, and the spacer in a polymer can also help toprovide an additional degree of sidechain mobility and placement inconjunction with backbone movement aided by groups that do notsterically hinder portions of the backbone from moving relative to oneanother. Further, a longer spacer helps to reduce the glass transitiontemperature and aid in drawability of a polymer film.

[0138] Thus, it is beneficial to have a spacer that is sufficiently longand flexible to allow mesogens on the same and/or adjoining polymers toassociate with one another, especially as a film of the polymer isdrawn. It is also beneficial to have a spacer that is not so shortand/or rigid that a substantial number of mesogens that have associatedare drawn away from each other, substantially reducing or eliminatingthe effect of the mesogens on birefringence. The spacer should not be solong that its properties become significant and affect or even dominatethe properties of the backbone.

[0139] Suitable spacers include saturated or unsaturated aliphaticgroups, aliphatic polyethers, siloxanes, aliphatic polyesters, aliphaticpolyamides, or other chain-like groups that space the mesogen away fromthe polymer backbone. Aliphatic spacers typically contain from one totwenty carbon atoms (e.g. methyl to didecyl), preferably from two to tencarbon atoms (e.g. ethyl to decyl), and more preferably from four to 10carbon atoms (e.g. butyl to decyl). Preferred spacers include saturatedaliphatic polyether chains having from 3 to 12 carbon atoms such aspolyethylene or polypropylene oxides. Other spacers having about thesame lengths as specified above are also preferred. Other preferredspacers include polyalkylenes having from 2 to 12 carbon atoms,polyperfluoroalkylenes having from 2 to 12 carbon atoms, andpolysiloxanes having from 2 to 12 silicon atoms.

[0140] Further Discussion of the Polymer

[0141] The polymer is preferably amorphous or substantially amorphous sothat an optical signal passes through the waveplate without a degree ofattenuation or scattering that degrades the performance of the PLCoptical device (such as substantially increasing optical loss) or causesproblems in detecting the optical signal with detection equipment (suchas optical sensors) positioned downstream of the polymer.

[0142] A waveplate or PLC in use may experience an elevated temperaturefor an extended period of time. Typically, these components are housedwithin enclosures that contain heat-generating electronic equipment, andoften the components are located where cooled air cannot be provided tothe components (such as in a pedestal in a residential or businessdistrict located in a desert). A PLC for telecommunications applicationis typically required to operate without failure in ambient environmentswith temperatures as high as 70° C. In some cases, such as most AWG's,the PLC is temperature stabilized at a temperature above this maximumambient temperature to avoid unwanted temperature fluctuations. Thisstabilization temperature typically is at or below 85° C. Thus it isdesirable that any waveplate used in a PLC can be subject to 85° C.temperature for the lifetime of the PLC without degradation in theoptical performance of the waveplate. As the temperature of a polymerwaveplate gets near (within about 10-20° C.) the glass transitiontemperature of the polymer, a process called relaxation occurs, in whichthe heat causes a transition from a glassy state to a more liquid state.This enables motion of the polymer chains and reduces or eliminates theorientation imparted by the strain/stresss, degrading its opticalperformance. As a rule of thumb, a polymer waveplate should be able towithstand temperatures about 40° C. below the polymer's glass transitiontemperature without degradation of optical properties, and higher glasstransition temperatures will mean increased resistance to heat.Therefore, the glass transition temperature of the polymer is preferablyat least about 125 C., and more preferably at least about 150 C. A glasstransition temperature as specified helps to assure that the opticalproperties of the waveplate or PLC do not degrade substantially over aperiod of years by assuring that the polymer does not “melt” or haveareas which undergo a phase transition that can allow polymer moleculesto move relative to one another, potentially changing the birefringence.

[0143] The polymer used to make a waveplate or PLC of the invention ispreferably selected to have a glass transition temperature of no morethan about 300 C., and preferably the glass transition temperature is nomore than about 250 C. Such polymer is easy to process into waveplatesreliably and repeatably, without degrading the polymer itself. A polymerwith a glass transition temperature of at least 300 C. is more difficultto stretch repeatably and controllably, especially where the polymer isundergoing a polymerization reaction such as imidization simultaneouslywith stretching. The preferred polymer used in waveplates and PLCs ofthe invention is completely reacted (e.g. imidized) prior to stretching,and since the glass transition temperature is less than 300 C. for thispolymer, polymer stretching can be controlled easily, and birefringenceis repeatable each time a film of material is stretched.

[0144] Mesogens and any associated spacers typically act as aplasticizer to reduce the glass transition temperature of the waveplatepolymer and therefore decrease the temperature required for drawabilityof the polymer (especially when attached to the backbone through anoptional linking group). Consequently, in many instances the backboneportion of the waveplate polymer may be formed of a polymer that has ahigh glass transition temperature and/or is more difficult to draw inthe absence of mesogens, and the incorporation of mesogens into thepolymer reduces the glass transition temperature to below the preferredmaximum glass transition temperature and/or improves drawability.

[0145] A polymer used to form a waveplate or PLC of the inventionpreferably can be stretched to a sufficient elongation at convenientlyachievable temperatures to achieve the desired birefringence withouttearing or degrading.

[0146] Preferably, when compared to a non-mesogen-containing butotherwise identical polymer, the mesogen-containing polymer used to forma waveplate or PLC of the invention has a reduced glass-transitiontemperature and improved drawability at a given temperature (as measuredby the amount a polymer film can be stretched without tearing the film).Preferably, it will also have increased birefringence across the planeof the film upon uniaxially drawing a film. Often the birefringence of afilm increases approximately linearly with increase in length duringstretching as illustrated in FIG. 1 (presumably as increased stretchingleads to increased molecular chain alignment while mesogens interact andhelp maintain alignment), and often the increase in birefringence beginsto level off as the film is stretched to high degrees of elongation. Themesogen-containing polymer also preferably may be drawn at a temperatureless than 300 C., which aids in processing the film without degradingit. In fact, the temperature at which the mesogen-containing polymer maybe drawn is often less than the glass transition temperature for thenon-mesogen-containing but otherwise identical polymer.

[0147] One knowledgeable in the art will understand that the polymermust have sufficiently high molecular weight to allow the necessarymechanical stability to be handled as a thin film, and subsequentlystretched to a sufficient birefringence without breaking or tearing. Thebirefringence attainable by a film generally increases with increasingmolecular weight (although this increase levels off for higher molecularweights), so a polymer of this invention must be made with sufficientlyhigh molecular weight to achieve the necessary birefringence for awaveplate. The molecular weight is preferably greater than 30,000 to100,000, depending on the polymer backbone, and is preferably not sohigh that the polymer becomes impractical to coat into a thin filmand/or draw to achieve high birefringence.

[0148] The polymer side-chain formed of the mesogen, linking group, andoptional spacer preferably aids in dissolving the polymer in a widerange of solvents. Although the specific solvents depend largely on thebackbone, mesogens usually broaden the range of solvents that can beused, often facilitating solubility in solvents such as ethers, ketones,esters, and chlorocarbons as well as the aprotic solvents such asN-methyl pyrrolidone which are required for rigid polyimides. Thisproperty allows a high-quality thin film to be easily cast from thesolution using well-known solution-based thin-film coating methods suchas spin coating, which film can be further stretched to induce in-planebirefringence prior to forming one or more waveplates of the inventionfrom the film.

[0149] In the '514 patent, it is stressed that the polymer must be veryrigid, and a strong preference is expressed for polymers that have nomore than two rotatable bonds (swivel bonds) per repeat unit. However,in the several examples in which even two swivel bonds exist, thepolymer is not capable of sufficient birefringence to make a waveplate.

[0150] A polymer used to form a waveplate or PLC of the invention ispreferably formed to have at least three swivel bonds per repeating unitof the backbone that permit portions of the backbone to rotate relativeto one another. Preferably, the polymer has at least four such bonds,more preferably five, and even more preferably six. For example, apolyetherimide as shown in FIG. 6 has two swivel bonds in each of thetwo ether linkages plus two swivel bonds in the isopropylidene linkage,giving a total of six swivel bonds in a repeating unit of the backboneabout which portions of the backbone may rotate. For this polymer, arepeat unit is defined herein as the bis-ADA linked to C6BP (thebiphenyl moiety having mesogenic side-chains) or the bis-ADA linked toPFMB (the 2,2′-bis(trifluoromethyl)biphenyl moiety).

[0151] The spacers in the sidechains of this polymer are also preferablyquite flexible, having numerous points about which the rigid mesogens(e.g. the biphenyl groups of the side chains illustrated in FIG. 6) mayrotate. In the polymer illustrated in FIG. 6, a biphenyl group mayrotate as a unit about the oxygen atom to which it is attached. Theoxygen atoms and methylene units of sidechains are free to move aboutadjacent methylene units, and the methylene units closest to thebackbone are free to rotate about the oxygen atoms of the esters towhich the methylenes are attached. The sidechains have a high degree offlexibility, and consequently the sidechains can flex and move to allowthe mesogens to associate. Because the mesogens are similar or identicalin structure as well as properties and because the mesogens aresignificantly different in structure and properties from e.g. the spacerand the backbone, it is believed that the mesogens associate to formmicrodomains within the polymer.

[0152] In addition to the presence of the mesogens, the polymer may befurther substituted or unsubstituted. If substituted, the substituentspreferably do not hinder the film from becoming more birefringent whendrawn. Typical substituents include groups such as alkyl, alcoxy, aryl,aralkyl, ester, cyano, nitro, or halogens such as chlorine or fluorine.The backbone, linker, spacer, and/or mesogen may be substituted.

[0153] One particularly preferred polymer is:

[0154] (bis-ADA)₀ ₅(PFMB_(y)C6BP_(1−y))₀ ₅,

[0155] where y is a number between 0 and 0.25, inclusive. Bis-ADA is4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride)represented by the following formula:

[0156] and PFMB is 2,2′-bis(trifluoromethyl)benzidine represented by thefollowing formula:

[0157] and C6BP (also known as C6PH) isbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylaterepresented by the following formula:

[0158] The polymer is a random copolymer, in which the C6BP moiety isditributed randomly along the polymer. A particularly preferred polymerfor use is that described by the formula above where y=0.2, asrepresented in FIG. 6.

[0159] Another particularly preferred polymer is the random copolymer:

[0160] (bis-A_(1−x)6FDA_(x))_(0.5)(PFMB_(y)C6BP_(1−y))_(0.5)

[0161] where x is a number between 0 and 0.5, inclusive, and y is anumber between 0 and 0.25, inclusive. A particularly preferred polymerfor use is that described by the formula above, where x=0.1 and y=0.2.6FDA is 4,4′-(hexafluoroisopropylidene) diphthalic anhydride representedby the following formula:

[0162] Another particularly preferred polymer is:

[0163] (PFMB_(0.5)IPC_(0.5))_(x)(C6BP_(0.5)IPC₀ ₅)_(y)

[0164] where y is a value between 0.05 and 0.5 and x=1−y. IPC isisophtlatic chloride represented by the following formula:

[0165] This produces a polyamide random copolymer. A particularlypreferred polymer for use is that described by the formula above, wherex=0.8 and y=0.2, as illustrated in FIG. 7.

[0166] Another polymer that may be useful in the practice of theinvention is:

[0167] (PFMB₀ ₅TPA_(0.5))_(x)(C6BP₀ ₅TPA_(0.5))_(y)

[0168] where y is a value between 0.05 and 0.5 and x=1−y. TPA isterephthalic acid represented by the following formula:

[0169] This produces a polyamide random copolymer as illustrated in FIG.12.

[0170] This same polymer can also be made using terephthalic chloride(TCA) instead of TPA, with reaction conditions modified accordingly. TCAis terephthalic chloride represented by the following formula:

[0171] Another polymer that may be useful in the practice of theinvention is:

[0172] (PFMB_(0.5)DPA_(0.5))_(x)(C6BP₀ ₅DPA_(0.5))_(y)

[0173] where y is a value between 0.05 and 0.5 and x=1−y. DPA isdiphenic acid represented by the following formula:

[0174] The polymer may be formed by conventional methods used to formother polymers containing mesogens. Consequently, the mesogen-containingpolymers may be formed by polymerizing monomers that have mesogensattached, or the polymers may be formed by polymerizing monomers havingreactive side-chains and reacting mesogen-containing compounds with thereactive side-chains.

[0175] Preferably, the polymers used to make waveplates of the inventionrequire no further reaction to complete the polymers during or afterdrawing. Certain polymers as disclosed in examples of the '514 patentdiscussed above must be drawn starting as poly(amic acid) films andimidized after or during the drawing process. The '514 patent teachesthat “performing the drawing for a polyimide film which is alreadyimidized and has no in-plane birefringence is ineffective since theconsequent in-plane birefringence is small. . . . ” It is believed thatreacting the polymer (in this case imidizing) during or after drawingdecreases the repeatability of the final birefringence. The need forpolymer reaction also can increase the number of steps in themanufacturing process, increasing cost and reducing yields. In addition,in the case of polyimides, imidization performed while the film is undertensile stress may proceed incompletely, leading to an increasedsensitivity of the film to water. In the present invention, certainexamples are disclosed of performing drawing of a polymer film which isalready imidized and has no in-plane birefringence, with such drawingresulting in a high birefringence suitable for use as waveplates.

[0176] Preferably, the polymers used to make waveplates of the inventioncan be drawn without appreciable solvent in the film. Certain polymersas disclosed in examples of the '514 patent discussed above are drawnwith a certain amount of solvent in the poly(amic acid) film, presumablyto plasticize the film and allow the rigid poly(amic acid) film to bemore readily drawn. In practice it is difficult to control the exactamount of solvent in a film, and thus it is believed that this decreasesthe repeatability of achieving the desired birefringence from such afilm.

[0177] Often polymers having mesogen-containing sidechains are notconstrained to be stretched in a partially-reacted state or with solventin the film because they can be easily drawn in their fully-reacted format temperatures well below 300° C. to achieve the high degree ofbirefringence necessary for waveplates. The mesogens increase thedrawability of the polymer, allowing the fully-reacted polymer to beheated and drawn in a single step to create sufficient birefringencewith a very high degree of repeatability and uniformity.

[0178] Waveplate manufacturing processes that involve self-shrinkingfilms, or involve drawing films with appreciable solvent content, orinvolve reactions such as imidizing after stretching may have morevariability and may be hard to control. Such films may require in-situmonitoring of birefringence during the drawing process, or additionalprocesses to fine-tune the birefringence after the drawing process.Preferably, waveplates of the invention can be drawn to a desiredbirefringence value at reasonable temperatures below 300° C. withoutneed for subsequent fine-tuning, and without the need for in-situmonitoring of the drawing or fine-tuning processes.

[0179] A waveplate formed using a polymer as described above may be moreresistant to heat and to humidity. The polymer may contain few groupsthat react with or associate with water, even under elevatedtemperatures. Further, the lower processing temperature (i.e. below 300C.) made possible by certain polymers of the invention helps to preventwater vapor from reacting with or associating with components of thepolymer, thus helping to assure resistance to heat and humidity.

[0180] A waveplate for a PLC is formed by making a thin polymer film ofsuitable thickness that the finished waveplate may fit into a thincavity (about 30 μm thick or less), cut or etched into the PLC, thelength of the cavity bridging a waveguide or waveguides of interest on aPLC and the width or height of the cavity (i.e. distance into theinterior of the PLC from the outer surface of the PLC that is parallelto the waveguides of the PLC) being sufficient to cut across the heightof the waveguides of interest. The thin polymer film is thus typicallyless than 30 μm thick. Although the cavity in the PLC is typically50-300 μm in height, the waveplate is typically 1-3 mm tall for ease ofhandling during insertion into the cavity.

[0181] The film is preferably formed from a liquid solution of thepolymer in solvent by methods of solvent casting known in the art (usingwirewound rod, doctor blade, Bird applicator, or spin coating, forinstance) onto a suitable substrate such as a silicon wafer or glassplate. The film is preferably made quite large for ease of handling andincreased uniformity, formed on a substrate typically 6-12 inches indiameter for a round substrate, or 6-12 inches per side for arectangular substrate. The film is properly dried to substantiallyremove the solvent, (e.g. by heating) and peeled from the substrate. Arelease agent may be used on the substrate to allow the film to beeasily separated from the substrate. A solvent or water may be used toaid in separating the film from the substrate. Alternatively, the filmcan be made directly from polymer without a substrate using methods suchas blow-forming or extrusion.

[0182] The film is then cut to an appropriate size for a stretchingapparatus. It is heated to a desired temperature, typically within 20°C. of the glass transition temperature, and stretched uniaxially orbiaxially using conventional techniques to obtain a thin polymer film ofthe desired thickness and birefringence. It is simplest, and thuspreferable, that the film thickness is chosen such that the film can bestretched uniaxially to achieve the desired bireflingence and thickness.Alternatively a thicker film can be made and stretched biaxially (withdifferent amounts of stretch along each of the two axes) to achieve thedesired birefringence and thickness. It is postulated that the polymerchains generally align along the axis of the direction of greateststretch (the “x” direction in the plane of the film, with the “y”direction being in the plane of the film and orthogonal to the “x”direction and the “z” direction being orthogonal to both the “x” and “y”directions). This generally provides a film in which the refractiveindex in the “x” direction is greater than the refractive index in the“y” direction, both of which are generally different from the refractiveindex in the “z” direction. Thus, light traveling generally along the“z” axis encounters birefringence caused primarily by the differentrefractive indices in the “x” and “y” axes.

[0183] The waveplate of the invention is typically biaxiallybirefringent. Such waveplates, as described above, exhibit a differencein refractive index along each of the x, y, and z axes of the film. Bycontrast, films of polymers as produced for liquid crystal displaycompensation layers are typically uniaxially birefringent because thesefilms have a constant refractive index along two of the axes (typicallythe x and y axes in the plane of the film), and a differing refractiveindex along the third axis (typically the z axis perpendicular to theplane of the film, along which light is transmitted).

[0184] Alternatively, the polymer can be solvent-cast onto a continuoussubstrate consisting of another polymer (such as polycarbonate) or ametal belt, using a continuous-roll solvent-casting and dryingapparatus. In such a system it is possible to delaminate the polymer webfrom the substrate and uniaxially stretch the polymer web in the sameapparatus. In this way a continuous roll of polymer of the desiredbirefringence and thickness can be formed.

[0185] After the polymer film is stretched, it is typically less than 30μm thick, more typically 10-15 μm thick, with birefringence necessary toachieve quarter waveplate or half waveplate function at the desiredoperating wavelength.

[0186] After the thin polymer film is stretched to the desiredbirefringence and thickness, it is then cut using a blade or shear,stamp or punch, laser, or another conventional technique to form thewaveplate. The waveplate is cut from the film at an angle appropriatefor the desired use of the waveplate. For the typical uses of rotatingTE to TM and TM to TE polarizations in a PLC using a half waveplate, orchanging linear polarizations to circular polarizations and circularpolarizations to linear polarizations in a PLC using a quarterwaveplate, this angle is 45° from the “x” axis, or stretch axis, of thefilm. While the invention is not limited to the following dimensions, awaveplate suitable for a PLC having an arrayed waveguide gratingtypically has a thickness of about 15 μm, a height of about 2 mm, and alength of about 8 mm. The length of a waveplate suitable for use in aPLC typically is between 1 mm and 15 mm, more typically between 5 mm and10 mm, the height is typically between 1 mm and 3 mm, and the thicknessis as discussed previously.

[0187] Preferably, the waveplate of the invention is capable of largepolarization conversion ratios. That is, if linearly-polarized lightincident upon a waveplate with its fast axis oriented at 45 degrees tothe polarization of the incoming light, and an analyzer is used todetect the optical energy polarized perpendicular to and parallel to thepolarization direction of the incident beam, the ratio of these opticalenergies is large. Preferably this ratio is greater than 25 dB, morepreferably greater than 30 dB.

EXAMPLES OF PLCS

[0188] The waveplate is inserted into the optical path of a waveguide.In some instances, a small channel is etched or cut or “diced” into oneor more waveguides of the PLC, and a transmissive waveplate is insertedinto the channel. In other instances, a reflective waveguide is attachedto the side of a substrate in the optical path of one or more waveguidesto form a reflective waveplate.

[0189]FIG. 8 illustrates an arrayed waveguide grating (AWG) 600 as anexample of a PLC into which a waveplate of the invention may beinserted. AWG 600, which is configured as a demultiplexer, has an inputwaveguide 610, a first lens or expansion region 620, an array of unequallength waveguides 630, a second lens 640, and multiple output waveguides650 that each receive an individual wavelength of light diffracted to itfrom the waveguides of the array through the second lens. Channel 660cut into the surface of the SiO₂ waveguides and cladding containstransmissive waveplate 670 made of a waveplate polymer as describedherein. The waveplate is generally positioned at or near the center ofthe waveguide array so that it compensates for the birefringence of thewaveguides of the array.

[0190] A wavelength multiplexer based on a Mach-Zehnder interferometer(MZI) is another PLC into which a waveplate of the invention may beinserted. FIG. 9 illustrates first 710 and second 720 input waveguides,first 730 and second 740 50% couplers, first 750 and second 760Mach-Zehnder arm waveguides, and first 770 and second 780 outputwaveguides. A waveplate of the invention 790 is inserted into thewaveguides of the MZI as illustrated to compensate for birefringence inthe SiO₂ waveguides of the MZI. A waveplate of the invention may be usedto form any of the optical devices illustrated in U.S. Pat. No.6,115,514, the disclosure of which is incorporated by reference in itsentirety herein.

EXAMPLES OF WAVEPLATES Example 1

[0191] A first waveplate polymer is formulated using 4 parts PFMB, 1part C6BP, and 5 parts bis-ADA in m-cresol to yield a random polymerhaving the general formula shown in FIG. 6. The copolymer is formedusing the following formulation.

[0192] PFMB (15.18 g, 47.41 mmol), C6BP (9.21 g, 11.86 mmol) andm-cresol (345 g) were added to a 500 ml three-necked round bottom flaskequipped with a mechanical stirrer, a nitrogen inlet, and a distillationhead. After the diamine monomers dissolved in m-cresol,4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (bis-ADA)(30.24 g, 58.10 mmol) was added and the mixture was stirred at roomtemperature for one day. Isoquinoline (0.5 ml) was added and thereaction temperature was raised to 202° C. for 15 hours. After thesolution was allowed to cool to room temperature, it was slowly added tomethanol to precipitate the polymer. The polymer was dissolved inchloroform and re-precipitated in methanol and dried in vacuum oven.

[0193] This waveplate polymer is formed into a film by dissolving thepolymer in a solvent such as cyclopentanone at 10-15% concentration,filtering the solution, and casting a sheet of approximately 20-40micron thickness using rod coating (Mayer) or Bird coating and dryingthe coating in an oven or on a hotplate. The glass-transitiontemperature of the film is measured to be Tg=155° C. The resultant sheetis heated to near or over its glass transition temperature and stretcheduniaxially at this temperature and at a rate of about 0.25 mm per secondto form a film. The film is cooled and tested, and waveplates are cutfrom the cooled film at a 45 degree angle to the stretch direction.

[0194]FIG. 1 illustrates the birefringence of this film as measured inthe x and y directions as a function of the amount that a small sectionat the center of the film has been stretched over its original size inthe x direction (“local elongation” (%)). The birefringence increasesmonotonically with amount of stretch, and the amount of increase issufficiently high to make a 15 μm thick half waveplate at 1550 nmwavelength. From this information, on can calculate the desired localelongation for any desired waveplate thickness. FIG. 2 shows thecalculated thickness of a half waveplate at 1550 nm wavelength and aquarter waveplate at 1550 nm wavelength as a function of the localelongation. Thus a half waveplate for 1550 nm wavelength can be createdwith thickness ranging from above 30 μm to below 10 μm.

Example 2

[0195] A polymer film is formed, and heated and stretched according toExample 1. After the film is stretched it is annealed in an oven at 145°C. for two hours. The thickness of the pre-stretched film and the degreeof elongation during the stretch are chosen such that after the film isstretched and annealed, the thickness of the film is approximately 15.6μm, and the retardance is one half wave at a wavelength of about 1550nm. A waveplate is cut from the film at a 45 degree angle to the stretchdirection. The waveplate is tested by illuminating it with polarizedlight at approximately 1550 nm wavelength polarized along the directionof the cut of the waveplate (and thus at about a 45 degree angle to thestretch axis of the waveplate). The light that is transmitted throughthe waveplate is passed through a polarizer used as an analyzer. Theoptical power transmitted through the analyzer is measured with theanalyzer perpendicular to the polarization of the input laser light, andagain with the analyzer parallel to the polarization of the input light.The ratio of these two measurements is found to be 31.9 dB. Thisdemonstrates that this film functions as a half waveplate and makes apolarization rotator with high extinction ratio.

Example 3

[0196] Two waveplates according to Example 2 are formed, one withretardance 0.47 waves and one with retardance 0.67 waves at about 1550nm wavelength. The waveplates are tested for birefringence and thenbaked on a hotplate at 125° C. for 2 hours, retested, and then bakedseveral more times, being retested after 8, 24, 48, 96, 192, and 288hours on the hotplate at 125° C. During this test, no measurable changesare detected in waveplate retardance, demonstrating that the waveplatesare thermally stable up to 125° C.

Example 4

[0197] Twelve waveplates are formed according to Example 2 each withbirefringence of about 0.5 waves at about 1550 nm wavelength andmeasured for retardance. The first four waveplates are exposed to 85° C.at 85% relative humidity (RH) for 500 hours, being measured after 24,120, and 500 hours. No measurable changes in retardance are detected,indicating that the waveplates are stable under high heat and humidity.The second four waveplates are exposed to 122° C., 98% RH, and 2atmospheres of pressure for 24 hours, being measured after 8 and 24hours. No measurable changes in retardance are detected, indicating thatthe waveplates are stable under very high heat, humidity, and pressure.The last four waveplates are exposed to thermal shock, being alternatelyexposed to 0° C. and 100° C. temperatures for 15 cycles. The waveplatesare measured after the 15 cycles, and no measurable changes inretardance are detected, indicating that the waveplates are stable underthermal shock.

Example 5

[0198] Eight arrayed-waveguide grating (AWG) chips are prepared usingsilica-on-silicon PLC technology. They are then tested for allperformance parameters typically associated with AWG devices, includinginsertion loss (IL), polarization dependent loss (PDL), uniformity,ripple, adjacent isolation, non-adjacent isolation, total isolation, andpolarization-dependent center-wavelength shift (PDW). Grooves about 20μm wide are cut into the chips in the center of the AWG grating using adicing saw. Eight half waveplates at 1550 nm wavelength about 15 μmthick are formed according to Example 2 and glued into the diced groovesof the AWG chips. All chips are then retested for the same performanceparameters and it is found that the waveplates significantly improve PDLand PDW, thus showing that the waveplates compensate for birefringencein the PLC AWG. The first four chips are then exposed to 122° C., 98%RH, and 2 atmospheres of pressure for 68 hours, being remeasured for thesame performance parameters after 8 and 68 hours. No measurable changesattributed to the waveplate are detected, indicating that the waveplatesof this invention, when inserted into AWG chips, are stable under veryhigh heat, humidity, and pressure. The second four chips are exposed tothermal shock, being alternately exposed to 0° C. and 100° C.temperatures for 100 cycles. The chips are remeasured for the sameperformance parameters after the 100 cycles, and no measurable changesare detected, indicating that the waveplates of this invention, wheninserted into AWG chips, are stable under thermal shock. The same secondfour chips are then exposed to 85° C. at 85% RH for 500 hours, beingremeasured for the same performance parameters after 214 and after 500hours. No measurable changes are detected, indicating that thewaveplates of this invention, when inserted into AWG chips, are stableunder high heat and humidity.

Example 6

[0199] Nine pre-tested arrayed-waveguide grating (AWG) chips, each witha half waveplate of this invention glued into the chip according toExample 5, are prepared. Optical fiber ribbons are attached to the chipsand the chips are fully packaged, including temperature stabilization,using processes well-known in the PLC industry. These packaged AWGdevices are then tested for all performance parameters typicallyassociated with AWG devices as in Example 4. Once again it is found thatthe waveplates compensate for birefringence in the AWG devices. Thefirst four packaged AWGs are then exposed to 85° C. at 85% RH for 500hours and are remeasured for the same performance parameters. Nomeasurable changes are detected, indicating that the waveplates of thisinvention, when inserted into AWG chips and packaged, are stable underhigh heat and humidity. The second four packaged AWGs are exposed tothermal cycles, each cycle consisting of successive exposure to −40° C.,21° C., 75° C., and 21° C. for 1 hour at each temperature, with atemperature rise and fall time of 0.95° C. per minute, repeating for 63cycles. The packaged AWG's are remeasured for the same performanceparameters after 42 and 63 cycles. No measurable changes are detected,indicating that the waveplates of this invention, when inserted into AWGchips and packaged, are stable under thermal cycling. The ninth packagedAWG is exposed to high laser power, by launching 2 watts of opticalpower at approximately 1480 nm wavelength into the input optical fiberof the AWG for a period of one week. The package AWG is then remeasuredfor the same performance parameters, and no measurable changes aredetected, indicating that the waveplates of this invention, wheninserted into AWG chips and packaged, are stable under high laser power.

Example 7

[0200] A second waveplate polymer is formulated using 5 parts IPC, 4parts PFMB, and 1 part C6BP, reacted in N-methylpyrrolidone (NMP) toform a polyamide random copolymer. The polymer is formed into a filmusing a method similar to the polymer Example 1. The glass-transitiontemperature is measured to be Tg=216° C. The resultant sheet is heatedto near or over its glass transition temperature and stretcheduniaxially at this temperature and at a rate of about 0.25 mm per secondto form a film. The film is cooled and tested, and waveplates are cutfrom the cooled film at a 45 degree angle to the stretch direction.

[0201]FIG. 3 illustrates the birefringence of this film as measured inthe x and y directions as a function of the amount that a small sectionat the center of the film has been stretched over its original size inthe x direction (“local elongation” (%)). The birefringence increasesmonotonically with amount of stretch, and the amount of increase issufficiently high to make a 15 μm thick half waveplate at 1550 nmwavelength. From this information, on can calculate the desired localelongation for any desired waveplate thickness. FIG. 4 shows thecalculated thickness of a half waveplate at 1550 nm wavelength and aquarter waveplate at 1550 nm wavelength as a function of the localelongation. Thus a half waveplate for 1550 nm wavelength can be createdwith thickness ranging from above 30 μm to below 12 μm.

Example 8

[0202] A polymer film is formed, and heated and stretched according toExample 7. After the film is stretched it is annealed in an oven at 145°C. for 3.5 hours. The thickness of the pre-stretched film and the degreeof elongation during the stretch are chosen such that after the film isstretched and annealed, the thickness of the film is approximately 16.3μm, and the retardance is one half wave at a wavelength of about 1550nm. A waveplate is cut from the film at a 45 degree angle to the stretchdirection. The waveplate is tested by illuminating it with polarizedlight at approximately 1550 nm wavelength polarized along the directionof the cut of the waveplate (and thus at about a 45 degree angle to thestretch axis of the waveplate). The light that is transmitted throughthe waveplate is passed through a polarizer used as an analyzer. Theoptical power transmitted through the analyzer is measured with theanalyzer perpendicular to the polarization of the input laser light, andagain with the analyzer parallel to the polarization of the input light.The ratio of these two measurements is found to be greater than 28 dB.This demonstrates that this film functions as a half waveplate and makesa polarization rotator with high extinction ratio.

Example 9

[0203] A third waveplate polymer is formulated using 1 part bis-ADA and1 part C6BP using processing analogous to that of Example 1. Thewaveplate polymer is dissolved in NMP at 3-5% concentration and madeinto a thin film by depositing the polymer solution on a glass substrateand baking out the solvent on a covered hotplate. The film is drawnuniaxially at 90 C. to three times its starting length (i.e. draw ratioof 200%), and the stretched film having a thickness of 14 micron isalmost transparent. The refractive indices in the plane of the filmparallel and perpendicular to the stretch direction are measured in aprism coupler manufactured by Metricon at wavelength 633 nm. In thestretch direction the refractive index is measured twice, giving valuesof 1.7116 and 1.7122. In the direction perpendicular to the stretchdirection the refractive index is again measured twice, giving values of1.6135 and 1.6137. From this the birefringence wavelength is calculatedto be 0.098, indicating that the polymer has achieved highbireflingence. The birefringence of the film at 1550 nm is estimated tobe 0.094. Thus with this amount of stretch, this polymer is suitable fora half waveplate at 1550 nm with 8.3 μm thickness.

Example 10

[0204] A polymer waveplate is formed using the polymer and procedure ofExample 9, but the waveplate polymer is drawn uniaxially at 100° C. totwice its starting length (i.e. draw ratio of 100%), and the stretchedfilm having a thickness of 9.5-10 microns is transparent and colorless.The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6941 and1.6941. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.6128 and1.6128. From this the birefringence at 633 nm wavelength is calculatedto be 0.081. The retardance of the film is subsequently measured atwavelength of about 1550 nm to be 0.45 waves. The birefringence at 1550nm is thus calculated to be 0.070. Thus with this amount of stretch,this polymer is suitable for a half waveplate at 1550 nm with 11.1 μmthickness.

Example 11

[0205] A polymer waveplate is formed using the polymer and procedure ofExample 10, but the waveplate polymer is drawn to a draw ratio of 80%.The thickness of the film prior to stretching is 16 micron, and thethickness after stretching is 10 micron. The film is transparent andcolorless. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6910 and1.6908. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.6152 and1.6152. From this the birefringence at 633 nm is calculated to be 0.076,indicating that the polymer has achieved high birefringence. Theretardance of the film is subsequently measured at wavelength of about1550 nm to be 0.36 waves. The birefringence at 1550 nm is thuscalculated to be 0.056. Thus with this amount of stretch, this polymeris suitable for a half waveplate at 1550 nm with 13.9 μm thickness.

Example 12

[0206] A fourth waveplate polymer is formulated of 4 parts 6FDA, 3 partsPFMB, and 1 part C6BP, and the waveplate polymer is drawn uniaxially inthe x direction at 200 C. to a draw ratio of 100% and a thickness of 12micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6111 and1.6112. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.5567 and1.5569. From this the birefringence at 633 nm is calculated to be 0.054,indicating that the polymer has achieved high birefringence. Thebirefringence of the film at 1550 nm is estimated to be 0.052. Thus withthis amount of stretch, this polymer is suitable for a half waveplate at1550 nm with 15 μm thickness.

Example 13

[0207] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 210 C. to a draw ratio of 100% and a thickness of 12micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6215 and1.6222. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.5540 and1.5560. From this the birefringence at 633 nm is calculated to be 0.067,indicating that the polymer has achieved high birefringence. Thebirefringence of the film at 1550 nm is estimated to be 0.064. Thus withthis amount of stretch, this polymer is suitable for a half waveplate at1550 nm with 12.2 μm thickness.

Example 14

[0208] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 215 C. to a draw ratio of 100% and a thickness of 13micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6156 and1.6152. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.5571 and1.5571. From this the birefringence at 633 nm is calculated to be 0.058,indicating that the polymer has achieved high birefringence. Thebirefringence of the film at 1550 nm is estimated to be 0.055. Thus withthis amount of stretch, this polymer is suitable for a half waveplate at1550 nm with 14 μm thickness.

Example 15

[0209] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 220 C. to a draw ratio of 80% and a thickness of 12.5micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured twice, giving values of 1.6159 and1.6158. In the direction perpendicular to the stretch direction therefractive index is again measured twice, giving values of 1.5542 and1.5545. From this the birefringence at 633 nm is calculated to be 0.062,indicating that the polymer has achieved high birefringence. Thebirefringence of the film at 1550 nm is estimated to be 0.058. Thus withthis amount of stretch, this polymer is suitable for a half waveplate at1550 nm with 13.2 μm thickness.

Example 16

[0210] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 230 C. to a draw ratio of 93.75% and a thickness of 14micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured multiple times, giving average value1.6098. In the direction perpendicular to the stretch direction therefractive index is again measured, giving average value 1.5622. Fromthis the birefringence at 633 nm is calculated to be 0.048, indicatingthat the polymer has achieved high birefringence. The retardance of thefilm is subsequently measured at wavelength of about 1550 nm to be 0.38waves. The birefringence at 1550 nm is thus calculated to be 0.042. Thuswith this amount of stretch, this polymer is suitable for a halfwaveplate at 1550 nm with 18.3 μm thickness.

Example 17

[0211] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 230 C. to a draw ratio of 110% and a thickness of 14micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured multiple times, giving average value1.6207. In the direction perpendicular to the stretch direction therefractive index is again measured, giving average value 1.5600. Fromthis the birefringence at 633 nm is calculated to be 0.061, indicatingthat the polymer has achieved high birefringence. The retardance of thefilm is subsequently measured at wavelength of about 1550 nm to be 0.53waves. The birefringence at 1550 nm is thus calculated to be 0.059. Thuswith this amount of stretch, this polymer is suitable for a halfwaveplate at 1550 nm with 13.2 μm thickness.

Example 18

[0212] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 240 C. to a draw ratio of 107% and a thickness of 13.5micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured multiple times, giving average value1.6181. In the direction perpendicular to the stretch direction therefractive index is again measured, giving average value 1.5602. Fromthis the birefringence at 633 nm is calculated to be 0.058, indicatingthat the polymer has achieved high birefringence. The retardance of thefilm is subsequently measured at wavelength of about 1550 nm to be 0.47waves. The birefringence at 1550 nm is thus calculated to be 0.054. Thuswith this amount of stretch, this polymer is suitable for a halfwaveplate at 1550 nm with 14.2 μm thickness.

Example 19

[0213] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 230 C. to a draw ratio of 100% and a thickness of 16.5micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured multiple times, giving average value1.6104. In the direction perpendicular to the stretch direction therefractive index is again measured, giving average value 1.5642. Fromthis the birefringence at 633 nm is calculated to be 0.046, indicatingthat the polymer has achieved high birefringence. The retardance of thefilm is subsequently measured at wavelength of about 1550 nm to be 0.41waves. The birefringence at 1550 nm is thus calculated to be 0.047. Thuswith this amount of stretch, this polymer is suitable for a halfwaveplate at 1550 nm with 16.3 μm thickness.

Example 20

[0214] A waveplate polymer is formulated 4 parts 6FDA, 3 parts PFMB, and1 part C6BP, and the waveplate polymer is drawn uniaxially in the xdirection at 230 C. to a draw ratio of 107% and a thickness of 14micron. The refractive indices in the plane of the film parallel andperpendicular to the stretch direction are measured in a prism couplermanufactured by Metricon at wavelength 633 nm. In the stretch directionthe refractive index is measured multiple times, giving average value1.6153. In the direction perpendicular to the stretch direction therefractive index is again measured, giving average value 1.5579. Fromthis the birefringence at 633 nm is calculated to be 0.057, indicatingthat the polymer has achieved high birefringence. The retardance of thefilm is subsequently measured at wavelength of about 1550 nm to be 0.47waves. The birefringence at 1550 nm is thus calculated to be 0.054. Thuswith this amount of stretch, this polymer is suitable for a halfwaveplate at 1550 nm with 14.4 μm thickness.

Example 21

[0215] A fifth waveplate polymer is formulated 9 parts bis-ADA, 1 part6FDA, 8 parts PFMB, and 2 parts C6BP, and the waveplate polymer is drawnuniaxially in the x direction at 190 C. to a draw ratio of 50% and athickness of 12 micron. The retardance of the film is subsequentlymeasured at wavelength of about 1550 nm to be 0.5 waves. Thebirefringence at 1550 nm is thus calculated to be 0.065.

Example 22 Preparation of PFMB (FIG. 10) 2-Iodotrifluoromethylbenzene(1)

[0216] A 4-L beaker, equipped with a mechanical stirrer, a thermometerand an addition funnel was charged with 560 ml of concentratedhydrochloric acid and 640 g of ice. After the mixture was stirred andcooled to 0° C., 250 ml of 2-trifluoromethylaniline (2.00 mol) was addedslowly. After the addition was complete, the mixture was stirred for 10minutes, and 141.0 g of sodium nitrite in 400 ml of cold water was adderdropwise so as to maintain the temperature below 0° C. The reactionmixture was stirred at 0° C. for an additional 30 minutes and thenfiltered. The filtrate, which was maintained at 0° C., was addeddropwise to a 4-L beaker charged with 381.2 g of potassium iodide in1000 ml of water cooled to 0° C. After the addition, the reactionmixture was stirred for an additional 30 minutes at 0° C. and then forone hour at room temperature. The mixture was placed in a separatoryfunnel, and the organic layer was separated. The water layer wasextracted with methylene chloride. The organic phase was washed with anaqueous sodium bisulfite solution several times and then dried overanhydrous magnesium sulfate. The solution was filtered and the methylenechloride was removed under reduced pressure to afford 510.9 g (94%) of apale orange oil.

2,2′-Bis(trifluoromethyl)biphenyl (2)

[0217] To a 2-L three-necked, round-bottom flask fitted with amechanical stirrer and a condenser was added 507.5 g of2-iodotrifluoromethylbenzene (1.86 mol), 282.0 g of copper powder and400 ml of DMF. The reaction mixture was stirred and heated at reflux for24 hours and filtered. The filtrate was distilled under reduced pressureto yield 211.8 g (78%) of a light yellow oil.

2,2′-Bis(trifluoromethyl)-4,4′-dinitrobiphenyl (3)

[0218] To a 2-L three-necked, round-bottom flask equipped with amechanical stirrer, a thermometer and an addition funnel was added 210.0g of 2,2′-bis(trifluoromethyl)biphenyl and 725.0 g of concentratedsulfuric acid. After the stirred mixture was cooled to room temperature,140.0 g of 70% concentrated nitric acid was added dropwise. After theaddition was complete, the reaction mixture was heated slowly to 140°C., and another 67 g of 70% concentrated nitric acid was added. Thereaction mixture was stirred at room temperature overnight and pouredinto ice water. The solid that precipitated was collected by filtrationand washed with water. The solid was recrystallized from acetone/ethanolto afford 199.1 g (72%) of light yellow crystals.

2,2′-Bis-(trifluoromethyl)4,4′-diaminobiphenyl (4, PFMB)

[0219] A hydrogenation bottle was charged with 40.0 g of2,2′-bis(trifluoromethyl)-4,4′-dinitrobiphenyl, 0.6 g of 5% palladium onactivated carbon and 200 ml of ethyl acetate. The bottle was secured ona Parr hydrogenation apparatus, flushed five times with hydrogen, andthen pressurized with hydrogen to 56 psi. The pressure was maintained,and the vessel was agitated for several hours. After the reactionmixture was filtered and about 200 ml of hexanes were added. Thecrystals that formed were filtered to afford 30.2 g (90%) of product.

[0220] Preparation of C6BP (FIG. 11)

6-Bromo-1-hexanol (5)

[0221] A mixture of 1,6-hexanediol (454.4 g, 3.84 mol), hydrobromic acid(48% wt, 651.3 g, 3.86 mol), and concentrated sulfuric acid (220.0 g)was stirred at room temperature for two days and then heated at refluxfor 3 hours. After the solution was allowed to cool to room temperature,the solution was extracted with methylene chloride three times. Theextract was washed with water several times and dried over magnesiumsulfate. The ethyl ether was removed on a rotary evaporator to give abrown liquid, which was chromatographed on a silica gel column withhexane as the eluent, and then with a mixture of ethyl acetate andhexane (1:1) as the eluent. The product fraction was collected and thesolvents were removed under reduced pressure to afford 291.3 g (42%) ofa light yellow clear liquid: ¹H-NMR (CDCl3) δ (ppm): 1.31-1.97 (m, 8H),3.38 (t, 2H), 3.61 (t, 2H).

4-(6-Hydroxyhexoxy)biphenyl (6)

[0222] To a 4 L three-necked round bottom flask fitted with a mechanicalstirrer and a condenser were added 125.0 g of 4-hydroxybiphenyl (0.734mol), 154.5 g of 6-bromo-1-hexanol (0.853 mol), 690 g of potassiumcarbonate, and 2500 ml of acetone. The reaction mixture was stirred andheated at reflux for 4 days and then filtered. The acetone was removedon a rotary evaporator, the residue was recrystallized from a mixture ofethyl acetate and hexanes to afford 188 g of white crystals (95%): mp92-94° C.; 1H-NMR (CDCl₃) δ (ppm) 1.30-1.84 (m, 8H), 3.65 (t, 2H), 3.99(t, 2H), 6.98 (d, 2H), 7.32-7.56 (m, 7H).

4,4′-Dinitrodiphenic Acid (7)

[0223] To a 1000 ml, three-necked, round-bottom flask equipped with amechanical stirrer, a thermometer and an addition funnel were added 30.0g of diphenic acid (2,2′-diphenyldicarboxylic acid) (0.123 mol) and 469g of concentrated sulfuric acid. After the diphenic acid dissolved toform a yellow solution, the mixture was cooled to −15° C. in a dry icebath. In a separate Erlenmeyer flask, concentrated nitric acid (70% wt,92.4 g, 1.03 mol) and concentrated sulfuric acid (12.0 g) were mixed andtransferred to the addition funnel. The acid mixture was added slowly tothe diphenic acid solution so that the mixture was maintained below 0°C. After the addition was complete, the reaction mixture was allowed towarm to room temperature and stirred for 24 hours. After the mixture waspoured onto crushed ice, the precipitate that formed was collected byfiltration and washed with water. The solid was dissolved in a 10%aqueous solution of sodium hydroxide, and the insoluble portion wasremoved by filtration. The filtrate was acidified with concentratedhydrochloric acid. The precipitate was collected and recrystallizedfirst from a mixture of ethanol and water twice to give 36.5 g of lightyellow crystals (89.5%); mp 255-258° C. (lit. mp 258-259° C.); 1H-NMR(DMSO-d6) δ (ppm) 7.53 (d, 2H), 8.44 (dd, 2H,) and 8.67 (d, 2H).

Bis{6-[4-biphenyloxy]hexyl}4,4′-dinitro-2,2′-biphenyldicarboxylate (8)

[0224] To a 500 ml Erlenmeyer flask fitted with a magnetic stirring barwere added 9.8 g of 4,4′-dinitrodiphenic acid (2) (29.6 mmol), 17.0 g of6-hydroxyhexoxybiphenyl (6) (62.8 mmol), 13.2 g ofdicyclohexylcarbodiimide (64.2 mmol), 0.5 g of dimethylaminopyridine,and 400 ml of methylene chloride. The mixture was stirred at roomtemperature overnight and filtered. The filtrate was taken to dryness ona rotary evaporator to give an orange solid. The solid wasrecrystallized from ethyl acetate/hexanes to afford 16.5 g (67%) oflight yellow crystals, mp: 121-122° C. ¹H-NMR (d-CDCl₃) δ (ppm) 1.2-1.8(m, 16H), 3.9 (t, 4H), 4.1 (t, 4H), 6.9 (d, 4H), 7.2-7.6 (m, 16H), 8.4(dd, 2H) and 8.9 (d, 2H).

Bis{6-[4-biphenyloxy]hexyl}4,4′-diamino-2,2′-biphenyldicarboxylate (9,C6BP)

[0225]Bis{6-[4-biphenyloxy]hexyl}4,4′-dinitro-2,2′-biphenyldicarboxylate (8)(2.26 g, 2.70 mol), palladium on activated carbon (5%, 0.31 g), andtetrahydrofuran (50 ml) were added to a hydrogenation bottle. The bottlewas secured on a Parr hydrogenation apparatus, flushed five times withhydrogen, then pressurized with hydrogen to 56 psi. The pressure wasmaintained and the vessel was agitated for 24 hours. After the reactionmixture was filtered and about 100 ml of hexanes were added torecrystallize the products directly to afford 1.7 g (80%) of lightyellow crystals. mp: 122-124° C. ¹H-NMR (CDCl₃) δ (ppm) 1.2-1.8 (m,16H), 3.9 (m, 8H), 6.8-7.6 (m, 24H). TABLE I Examples of backbones,mesogens, linkers, and optional spacers “X” GROUP “R” GROUP BACKBONE OFOF LINKER OPTIONAL SPACER DESIGNATION (“B”) MESOGEN MESOGEN (“L”) (“S”)1 polycarbonate (none) hydrogen ether poly(alkylene oxide) 2 polyolefinaxo alkyl ester polyalkane 3 polysulfone diazo cycloalkyl amidepolyperfluoroalkane 4 polyphenylene azoxy aryl imide polysiloxane 5polyimide nitrone aralkyl urethane aliphatic polyether 6 polyamideimidecarbon-carbon alkaryl alkylene double bond 7 polyesterimidecarbon-carbon cyano alkyl triple bond 8 polyetherimide amide alkoxy 9polyketone imide acyloxy 10 polyetherketone Schiff base halogen 11polybenz- ester oxazole 12 polyoxa-diazole 13 polybenzo- thiazole 14polythia-diazole 15 polyquin-oxaline 16 polybenz- imidazole 17polyacetal 18 polysulfone 19 polysulfide 20 polythioester 21 polysulfon-amide 22 polyamide 23 polyurethane 24 polyurea 25 polyimine 26 poly-phosphazene 27 polysilane 28 polysiloxane 29 polysilazane 30 polyether31 polycarbonate 32 polyester 33 polyphenylene 34 polydiene 35polyalkene 36 polyacrylate 37 polyvinyl ether 38 polyvinyl ketone 39polyvinyl halide 40 polyvinyl nitrile 41 polyvinyl ester 42 polystyrene43 polyarylether 44 polyarylene

[0226] TABLE 2 Polymers used to form waveplates polyimide backbone withphenyl-phenyl mesogen polyimide backbone with phenyl-phenyl-cyanomesogen polyimide backbone with phenyl-phenyl-acyloxy mesogen polyimidebackbone with phenyl-phenyl-alkyl mesogen polyimide backbone withphenyl-phenyl-aryl mesogen polyimide backbone with phenyl-C double bondC-phenyl mesogen polyimide backbone with phenyl-C double bondC-phenyl-cyano mesogen polyimide backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polyimide backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyimide backbone with phenyl-C double bondC-phenyl-aryl mesogen polyimide backbone with phenyl-C triple bondC-phenyl mesogen polyimide backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyimide backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polyimide backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polyimide backbone with phenyl-C triple bondC-phenyl-aryl mesogen polyimide backbone with phenyl-ester-phenylmesogen polyimide backbone with phenyl-ester-phenyl-cyano mesogenpolyimide backbone with phenyl-ester-phenyl-acyloxy mesogen polyimidebackbone with phenyl-ester-phenyl-alkyl mesogen polyimide backbone withphenyl-ester-phenyl-aryl mesogen polyimide backbone withphenyl-amide-phenyl mesogen polyimide backbone withphenyl-amide-phenyl-cyano mesogen polyimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyimide backbone withphenyl-amide-phenyl-alkyl mesogen polyimide backbone withphenyl-amide-phenyl-aryl mesogen polyimide backbone withphenyl-azo-phenyl mesogen polyimide backbone withphenyl-azo-phenyl-cyano mesogen polyimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyimide backbone withphenyl-azo-phenyl-alkyl mesogen polyimide backbone withphenyl-azo-phenyl-aryl mesogen polyetherimide backbone withphenyl-phenyl mesogen polyetherimide backbone with phenyl-phenyl-cyanomesogen polyetherimide backbone with phenyl-phenyl-acyloxy mesogenpolyetherimide backbone with phenyl-phenyl-alkyl mesogen polyetherimidebackbone with phenyl-phenyl-aryl mesogen polyetherimide backbone withphenyl-C double bond C-phenyl mesogen polyetherimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyetherimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyetherimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyetherimide backbonephenyl-C double bond C-phenyl-aryl mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyetherimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyetherimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyetherimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyetherimide backbonewith phenyl-ester-phenyl mesogen polyetherimide backbone withphenyl-ester-phenyl-cyano mesogen polyetherimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-ester-phenyl-alkyl mesogen polyetherimide backbone withphenyl-ester-phenyl-aryl mesogen polyetherimide backbone withphenyl-amide-phenyl mesogen polyetherimide backbone withphenyl-amide-phenyl-cyano mesogen polyetherimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-amide-phenyl-alkyl mesogen polyetherimide backbone withphenyl-amide-phenyl-aryl mesogen polyetherimide backbone withphenyl-azo-phenyl mesogen polyetherimide backbone withphenyl-azo-phenyl-cyano mesogen polyetherimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyetherimide backbone withphenyl-azo-phenyl-alkyl mesogen polyetherimide backbone withphenyl-azo-phenyl-aryl mesogen polyesterimide backbone withphenyl-phenyl mesogen polyesterimide backbone with phenyl-phenyl-cyanomesogen polyesterimide backbone with phenyl-phenyl-acyloxy mesogenpolyesterimide backbone with phenyl-phenyl-alkyl mesogen polyesterimidebackbone with phenyl-phenyl-aryl mesogen polyesterimide backbone withphenyl-C double bond C-phenyl mesogen polyesterimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyesterimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyesterimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyesterimide backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl mesogen polyesterimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyesterimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyesterimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyesterimide backbonewith phenyl-ester-phenyl mesogen polyesterimide backbone withphenyl-ester-phenyl-cyano mesogen polyesterimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-ester-phenyl-alkyl mesogen polyesterimide backbone withphenyl-ester-phenyl-aryl mesogen polyesterimide backbone withphenyl-amide-phenyl mesogen polyesterimide backbone withphenyl-amide-phenyl-cyano mesogen polyesterimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-amide-phenyl-alkyl mesogen polyesterimide backbone withphenyl-amide-phenyl-aryl mesogen polyesterimide backbone withphenyl-azo-phenyl mesogen polyesterimide backbone withphenyl-azo-phenyl-cyano mesogen polyesterimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyesterimide backbone withphenyl-azo-phenyl-alkyl mesogen polyesterimide backbone withphenyl-azo-phenyl-aryl mesogen polyamideimide backbone withphenyl-phenyl mesogen polyamideimide backbone with phenyl-phenyl-cyanomesogen polyamideimide backbone with phenyl-phenyl-acyloxy mesogenpolyamideimide backbone with phenyl-phenyl-alkyl mesogen polyamideimidebackbone with phenyl-phenyl-aryl mesogen polyamideimide backbone withphenyl-C double bond C-phenyl mesogen polyamideimide backbone withphenyl-C double bond C-phenyl-cyano mesogen polyamideimide backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyamideimide backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyamideimide backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl mesogen polyamideimide backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyamideimide backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyamideimide backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyamideimide backbonewith phenyl-ester-phenyl mesogen polyamideimide backbone withphenyl-ester-phenyl-cyano mesogen polyamideimide backbone withphenyl-ester-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-ester-phenyl-alkyl mesogen polyamideimide backbone withphenyl-ester-phenyl-aryl mesogen polyamideimide backbone withphenyl-amide-phenyl mesogen polyamideimide backbone withphenyl-amide-phenyl-cyano mesogen polyamideimide backbone withphenyl-amide-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-amide-phenyl-alkyl mesogen polyamideimide backbone withphenyl-amide-phenyl-aryl mesogen polyamideimide backbone withphenyl-azo-phenyl mesogen polyamideimide backbone withphenyl-azo-phenyl-cyano mesogen polyamideimide backbone withphenyl-azo-phenyl-acyloxy mesogen polyamideimide backbone withphenyl-azo-phenyl-alkyl mesogen polyamideimide backbone withphenyl-azo-phenyl-aryl mesogen polyketone backbone with phenyl-phenylmesogen polyketone backbone with phenyl-phenyl-cyano mesogen polyketonebackbone with phenyl-phenyl-acyloxy mesogen polyketone backbone withphenyl-phenyl-alkyl mesogen polyketone backbone with phenyl-phenyl-arylmesogen polyketone backbone with phenyl-C double bond C-phenyl mesogenpolyketone backbone with phenyl-C double bond C-phenyl-cyano mesogenpolyketone backbone with phenyl-C double bond C-phenyl-acyloxy mesogenpolyketone backbone with phenyl-C double bond C-phenyl-alkyl mesogenpolyketone backbone with phenyl-C double bond C-phenyl-aryl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-cyano mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-acyloxy mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-alkyl mesogenpolyketone backbone with phenyl-C triple bond C-phenyl-aryl mesogenpolyketone backbone with phenyl-ester-phenyl mesogen polyketone backbonewith phenyl-ester-phenyl-cyano mesogen polyketone backbone withphenyl-ester-phenyl-acyloxy mesogen polyketone backbone withphenyl-ester-phenyl-alkyl mesogen polyketone backbone withphenyl-ester-phenyl-aryl mesogen polyketone backbone withphenyl-amide-phenyl mesogen polyketone backbone withphenyl-amide-phenyl-cyano mesogen polyketone backbone withphenyl-amide-phenyl-acyloxy mesogen polyketone backbone withphenyl-amide-phenyl-alkyl mesogen polyketone backbone withphenyl-amide-phenyl-aryl mesogen polyketone backbone withphenyl-azo-phenyl mesogen polyketone backbone withphenyl-azo-phenyl-cyano mesogen polyketone backbone withphenyl-azo-phenyl-acyloxy mesogen polyketone backbone withphenyl-azo-phenyl-alkyl mesogen polyketone backbone withphenyl-azo-phenyl-aryl mesogen polyarylethers backbone withphenyl-phenyl mesogen polyarylethers backbone with phenyl-phenyl-cyanomesogen polyarylethers backbone with phenyl-phenyl-acyloxy mesogenpolyarylethers backbone with phenyl-phenyl-alkyl mesogen polyarylethersbackbone with phenyl-phenyl-aryl mesogen polyarylethers backbone withphenyl-C double bond C-phenyl mesogen polyarylethers backbone withphenyl-C double bond C-phenyl-cyano mesogen polyarylethers backbone withphenyl-C double bond C-phenyl-acyloxy mesogen polyarylethers backbonewith phenyl-C double bond C-phenyl-alkyl mesogen polyarylethers backbonewith phenyl-C double bond C-phenyl-aryl mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl mesogen polyarylethers backbone withphenyl-C triple bond C-phenyl-cyano mesogen polyarylethers backbone withphenyl-C triple bond C-phenyl-acyloxy mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl-alkyl mesogen polyarylethers backbonewith phenyl-C triple bond C-phenyl-aryl mesogen polyarylethers backbonewith phenyl-ester-phenyl mesogen polyarylethers backbone withphenyl-ester-phenyl-cyano mesogen polyarylethers backbone withphenyl-ester-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-ester-phenyl-alkyl mesogen polyarylethers backbone withphenyl-ester-phenyl-aryl mesogen polyarylethers backbone withphenyl-amide-phenyl mesogen polyarylethers backbone withphenyl-amide-phenyl-cyano mesogen polyarylethers backbone withphenyl-amide-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-amide-phenyl-alkyl mesogen polyarylethers backbone withphenyl-amide-phenyl-aryl mesogen polyarylethers backbone withphenyl-azo-phenyl mesogen polyarylethers backbone withphenyl-azo-phenyl-cyano mesogen polyarylethers backbone withphenyl-azo-phenyl-acyloxy mesogen polyarylethers backbone withphenyl-azo-phenyl-alkyl mesogen polyarylethers backbone withphenyl-azo-phenyl-aryl mesogen polyetherketone backbone withphenyl-phenyl mesogen polyetherketone backbone with phenyl-phenyl-cyanomesogen polyetherketone backbone with phenyl-phenyl-acyloxy mesogenpolyetherketone backbone with phenyl-phenyl-alkyl mesogenpolyetherketone backbone with phenyl-phenyl-aryl mesogen polyetherketonebackbone with phenyl-C double bond C-phenyl mesogen polyetherketonebackbone with phenyl-C double bond C-phenyl-cyano mesogenpolyetherketone backbone with phenyl-C double bond C-phenyl-acyloxymesogen polyetherketone backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyetherketone backbone with phenyl-C doublebond C-phenyl-aryl mesogen polyetherketone backbone with phenyl-C triplebond C-phenyl mesogen polyetherketone backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyetherketone backbone with phenyl-C triplebond C-phenyl-acyloxy mesogen polyetherketone backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen polyetherketone backbone withphenyl-C triple bond C-phenyl-aryl mesogen polyetherketone backbone withphenyl-ester-phenyl mesogen polyetherketone backbone withphenyl-ester-phenyl-cyano mesogen polyetherketone backbone withphenyl-ester-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-ester-phenyl-alkyl mesogen polyetherketone backbone withphenyl-ester-phenyl-aryl mesogen polyetherketone backbone withphenyl-amide-phenyl mesogen polyetherketone backbone withphenyl-amide-phenyl-cyano mesogen polyetherketone backbone withphenyl-amide-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-amide-phenyl-alkyl mesogen polyetherketone backbone withphenyl-amide-phenyl-aryl mesogen polyetherketone backbone withphenyl-azo-phenyl mesogen polyetherketone backbone withphenyl-azo-phenyl-cyano mesogen polyetherketone backbone withphenyl-azo-phenyl-acyloxy mesogen polyetherketone backbone withphenyl-azo-phenyl-alkyl mesogen polyetherketone backbone withphenyl-azo-phenyl-aryl mesogen polysulfone backbone with phenyl-phenylmesogen polysulfone backbone with phenyl-phenyl-cyano mesogenpolysulfone backbone with phenyl-phenyl-acyloxy mesogen polysulfonebackbone with phenyl-phenyl-alkyl mesogen polysulfone backbone withphenyl-phenyl-aryl mesogen polysulfone backbone with phenyl-C doublebond C-phenyl mesogen polysulfone backbone with phenyl-C double bondC-phenyl-cyano mesogen polysulfone backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polysulfone backbone with phenyl-C double bondC-phenyl-alkyl mesogen polysulfone backbone with phenyl-C double bondC-phenyl-aryl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-cyano mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polysulfone backbone with phenyl-C triple bondC-phenyl-aryl mesogen polysulfone backbone with phenyl-ester-phenylmesogen polysulfone backbone with phenyl-ester-phenyl-cyano mesogenpolysulfone backbone with phenyl-ester-phenyl-acyloxy mesogenpolysulfone backbone with phenyl-ester-phenyl-alkyl mesogen polysulfonebackbone with phenyl-ester-phenyl-aryl mesogen polysulfone backbone withphenyl-amide-phenyl mesogen polysulfone backbone withphenyl-amide-phenyl-cyano mesogen polysulfone backbone withphenyl-amide-phenyl-acyloxy mesogen polysulfone backbone withphenyl-amide-phenyl-alkyl mesogen polysulfone backbone withphenyl-amide-phenyl-aryl mesogen polysulfone backbone withphenyl-azo-phenyl mesogen polysulfone backbone withphenyl-azo-phenyl-cyano mesogen polysulfone backbone withphenyl-azo-phenyl-acyloxy mesogen polysulfone backbone withphenyl-azo-phenyl-alkyl mesogen polysulfone backbone withphenyl-azo-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-phenyl mesogen aromatic polysulfide backbone withphenyl-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-phenyl-aryl mesogen aromatic polysulfide backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polysulfide backbone with phenyl-Cdouble bond C-phenyl- cyano mesogen aromatic polysulfide backbone withphenyl-C double bond C-phenyl- acyloxy mesogen aromatic polysulfidebackbone with phenyl-C double bond C-phenyl-alkyl mesogen aromaticpolysulfide backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polysulfide backbone with phenyl-C triple bond C-phenyl mesogenaromatic polysulfide backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polysulfide backbone with phenyl-C triple bondC-phenyl- acyloxy mesogen aromatic polysulfide backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polysulfide backbonewith phenyl-ester-phenyl mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-ester-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-amide-phenyl-aryl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-cyano mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polysulfide backbone withphenyl-azo-phenyl-aryl mesogen polyarylene backbone with phenyl-phenylmesogen polyarylene backbone with phenyl-phenyl-cyano mesogenpolyarylene backbone with phenyl-phenyl-acyloxy mesogen polyarylenebackbone with phenyl-phenyl-alkyl mesogen polyarylene backbone withphenyl-phenyl-aryl mesogen polyarylene backbone with phenyl-C doublebond C-phenyl mesogen polyarylene backbone with phenyl-C double bondC-phenyl-cyano mesogen polyarylene backbone with phenyl-C double bondC-phenyl-acyloxy mesogen polyarylene backbone with phenyl-C double bondC-phenyl-alkyl mesogen polyarylene backbone with phenyl-C double bondC-phenyl-aryl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-cyano mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-alkyl mesogen polyarylene backbone with phenyl-C triple bondC-phenyl-aryl mesogen polyarylene backbone with phenyl-ester-phenylmesogen polyarylene backbone with phenyl-ester-phenyl-cyano mesogenpolyarylene backbone with phenyl-ester-phenyl-acyloxy mesogenpolyarylene backbone with phenyl-ester-phenyl-alkyl mesogen polyarylenebackbone with phenyl-ester-phenyl-aryl mesogen polyarylene backbone withphenyl-amide-phenyl mesogen polyarylene backbone withphenyl-amide-phenyl-cyano mesogen polyarylene backbone withphenyl-amide-phenyl-acyloxy mesogen polyarylene backbone withphenyl-amide-phenyl-alkyl mesogen polyarylene backbone withphenyl-amide-phenyl-aryl mesogen polyarylene backbone withphenyl-azo-phenyl mesogen polyarylene backbone withphenyl-azo-phenyl-cyano mesogen polyarylene backbone withphenyl-azo-phenyl-acyloxy mesogen polyarylene backbone withphenyl-azo-phenyl-alkyl mesogen polyarylene backbone withphenyl-azo-phenyl-aryl mesogen aromatic polyester backbone withphenyl-phenyl mesogen aromatic polyester backbone withphenyl-phenyl-cyano mesogen aromatic polyester backbone withphenyl-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-phenyl-aryl mesogen aromatic polyester backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polyester backbone with phenyl-Cdouble bond C-phenyl-cyano mesogen aromatic polyester backbone withphenyl-C double bond C-phenyl-acyloxy mesogen aromatic polyesterbackbone with phenyl-C double bond C-phenyl-alkyl mesogen aromaticpolyester backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polyester backbone with phenyl-C triple bond C-phenyl mesogenaromatic polyester backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polyester backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen aromatic polyester backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polyester backbonewith phenyl-ester-phenyl mesogen aromatic polyester backbone withphenyl-ester-phenyl-cyano mesogen aromatic polyester backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-ester-phenyl-aryl mesogen aromatic polyester backbone withphenyl-amide-phenyl mesogen aromatic polyester backbone withphenyl-amide-phenyl-cyano mesogen aromatic polyester backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-amide-phenyl-aryl mesogen aromatic polyester backbone withphenyl-azo-phenyl mesogen aromatic polyester backbone withphenyl-azo-phenyl-cyano mesogen aromatic polyester backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polyester backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polyester backbone withphenyl-azo-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-phenyl mesogen aromatic polyamide backbone withphenyl-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-phenyl-aryl mesogen aromatic polyamide backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polyamide backbone with phenyl-Cdouble bond C-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-C double bond C-phenyl- acyloxy mesogen aromatic polyamidebackbone with phenyl-C double bond C-phenyl- alkyl mesogen aromaticpolyamide backbone with phenyl-C double bond C-phenyl-aryl mesogenaromatic polyamide backbone with phenyl-C triple bond C-phenyl mesogenaromatic polyamide backbone with phenyl-C triple bond C-phenyl-cyanomesogen aromatic polyamide backbone with phenyl-C triple bondC-phenyl-acyloxy mesogen aromatic polyamide backbone with phenyl-Ctriple bond C-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-C triple bond C-phenyl-aryl mesogen aromatic polyamide backbonewith phenyl-ester-phenyl mesogen aromatic polyamide backbone withphenyl-ester-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-ester-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-ester-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-ester-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-amide-phenyl mesogen aromatic polyamide backbone withphenyl-amide-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-amide-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-amide-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-amide-phenyl-aryl mesogen aromatic polyamide backbone withphenyl-azo-phenyl mesogen aromatic polyamide backbone withphenyl-azo-phenyl-cyano mesogen aromatic polyamide backbone withphenyl-azo-phenyl-acyloxy mesogen aromatic polyamide backbone withphenyl-azo-phenyl-alkyl mesogen aromatic polyamide backbone withphenyl-azo-phenyl-aryl mesogen aromatic polycarbonate backbone withphenyl-phenyl mesogen aromatic polycarbonate backbone withphenyl-phenyl-cyano mesogen aromatic polycarbonate backbone withphenyl-phenyl-acyloxy mesogen aromatic polycarbonate backbone withphenyl-phenyl-alkyl mesogen aromatic polycarbonate backbone withphenyl-phenyl-aryl mesogen aromatic polycarbonate backbone with phenyl-Cdouble bond C-phenyl mesogen aromatic polycarbonate backbone withphenyl-C double bond C-phenyl- cyano mesogen aromatic polycarbonatebackbone with phenyl-C double bond C-phenyl- acyloxy mesogen aromaticpolycarbonate backbone with phenyl-C double bond C-phenyl- alkyl mesogenaromatic polycarbonate backbone with phenyl-C double bond C-phenyl- arylmesogen aromatic polycarbonate backbone with phenyl-C triple bondC-phenyl mesogen aromatic polycarbonate backbone with phenyl-C triplebond C-phenyl- cyano mesogen aromatic polycarbonate backbone withphenyl-C triple bond C-phenyl- acyloxy mesogen aromatic polycarbonatebackbone with phenyl-C triple bond C-phenyl- alkyl mesogen aromaticpolycarbonate backbone with phenyl-C triple bond C-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-cyano mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-acyloxy mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-alkyl mesogenaromatic polycarbonate backbone with phenyl-ester-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-cyano mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-acyloxy mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-alkyl mesogenaromatic polycarbonate backbone with phenyl-amide-phenyl-aryl mesogenaromatic polycarbonate backbone with phenyl-azo-phenyl mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-cyano mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-acyloxy mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-alkyl mesogen aromaticpolycarbonate backbone with phenyl-azo-phenyl-aryl mesogen

What is claimed is:
 1. A waveplate comprising a mesogen-containingpolymer film having a backbone and having sidechains containing mesogengroups, wherein the mesogen-containing polymer film has a length, awidth, and a thickness such that said mesogen-containing polymer film isinsertable into a channel in an optical pathway of the planar lightwavecircuit.
 2. A waveplate according to claim 1 wherein saidmesogen-containing polymer film has a birefringence sufficiently high torotate or convert a polarization state of an optical signal traversingthe optical pathway.
 3. A waveplate according to claim 2 wherein thebirefringence is at least 0.52.
 4. A waveplate according to claim 2wherein the waveplate is a half waveplate of thickness between 5 and 25μm.
 5. A waveplate according to claim 2 wherein the waveplate is aquarter waveplate of thickness between 5 and 25 μm.
 6. A waveplateaccording to claim 1 wherein the mesogen-containing polymer film isformed of a polymer having a glass transition temperature between 100 C.and 300 C.
 7. A waveplate according to claim 1 wherein the backbonecontains monomers having at least two groups that provide rotationalfreedom within the backbone.
 8. A waveplate according to claim 1 whereinthe waveplate has a warpage of less than 350 μm.
 9. A waveplateaccording to claim 1 wherein the backbone comprises a polymer selectedfrom the group consisting of: polyimides, polyetherimides,polyesterimides, polyamideimides, polyketones, polyarylethers,polyetherketones, polysulfones, polysulfides, polyarylenes, polyesters,polyamides, polycarbonates, polyolefins, polyvinylesters, polyurethanes,polyacrylates, polyphenylenes.
 10. A waveplate according to claim 9wherein the backbone comprises polyetherimide polymer.
 11. A waveplateaccording to claim 9 wherein the backbone comprises polyamide polymer.12. A waveplate according to claim 10 wherein the backbone is formed ofone or more components selected from the group consisting of4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride);4,4′-(hexafluoroisopropylidene) diphthalic anhydride;2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.
 13. Awaveplate according to claim 11 wherein the backbone is formed of one ormore components selected from the group consisting of isophthalicchloride; 2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).
 14. Awaveplate according to claim 13 wherein the backbone is formed ofisophthalic chloride; 2,2′-bis(trifluoromethyl)benzidine; andbis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate.
 15. Awaveplate according to claim 13 wherein the backbone is formed of2,2′-bis(trifluoromethyl)benzidine;bis{6-[4-biphenyloxy]hexyl}4,4′diamino-2-2′-biphenyldicarboxylate; and4,4′-bis(4,4′-isopropylidene diphenoxy)-bis(phthalic anhydride).
 16. Awaveplate according to claim 1 wherein the mesogen groups have the formphenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from the groupconsisting of azo, diazo, azoxy, nitrone, carbon-carbon double bond,carbon-carbon triple bond, amide, imide, Schiff base, and ester; and Ris selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.17. A waveplate according to claim 1 wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane, and trans 2,5 disubstituted 1,3 dioxathiane.18. A waveplate according to claim 9 wherein the mesogen groups have theform phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from thegroup consisting of azo, diazo, azoxy, nitrone, carbon-carbon doublebond, carbon-carbon triple bond, amide, imide, Schiff base, and ester;and R is selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.19. A waveplate according to claim 9 wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.20. A waveplate according to claim 1 wherein the mesogen group isbiphenyl.
 21. A waveplate according to claim 9 wherein the mesogen groupis biphenyl.
 22. A waveplate according to claim 10 wherein the mesogengroup is biphenyl.
 23. A waveplate according to claim 11 wherein themesogen group is biphenyl.
 24. A waveplate according to claim 1 whereinthe mesogen groups comprise at least two aromatic groups and wherein themesogen groups associate to help maintain birefringence as the film isdrawn.
 25. A waveplate according to claim 1 wherein the side chainscomprise linking groups linking the mesogen groups to the backbone,wherein the linking groups are selected from the group consisting of:ether, ester, amide, imide, urethane, alkylene, alkyl.
 26. A waveplateaccording to claim 9 wherein the side chains comprise linking groupslinking the mesogen groups to the backbone, wherein the linking groupsare selected from the group consisting of ether, ester, amide, imide,urethane, alkylene, alkyl.
 27. A waveplate according to claim 16 whereinthe side chains comprise linking groups linking the mesogen groups tothe backbone, wherein the linking groups are selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl. 28.A waveplate according to claim 17 wherein the side chains compriselinking groups linking the mesogen groups to the backbone, wherein thelinking groups are selected from the group consisting of ether, ester,amide, imide, urethane, alkylene, alkyl.
 29. A waveplate according toclaim 1 wherein the side chains further comprise spacing groups linkingthe mesogen groups to the linking groups, the spacing groups beingselected from the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 30. Awaveplate according to claim 9 wherein the side chains further comprisespacing groups linking the mesogen groups to the linking groups, thespacing groups being selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.
 31. A waveplate according to claim 16 wherein the side chainsfurther comprise spacing groups linking the mesogen groups to thelinking groups, the spacing groups being selected from the groupconsisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane,polysiloxane, and aliphatic polyether.
 32. A waveplate according toclaim 17 wherein the side chains further comprise spacing groups linkingthe mesogen groups to the linking groups, the spacing groups beingselected from the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 33. Awaveplate according to claim 20 wherein the side chains further comprisespacing groups linking the mesogen groups to the linking groups, thespacing groups being selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.
 34. A waveplate according to claim 22 wherein the side chainsfurther comprise spacing groups linking the mesogen groups to thelinking groups, the spacing groups being selected from the groupconsisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane,polysiloxane, and aliphatic polyether.
 35. A waveplate according toclaim 23 wherein the side chains further comprise spacing groups linkingthe mesogen groups to the linking groups, the spacing groups beingselected from the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 36. Awaveplate according to claim 24 wherein the side chains further comprisespacing groups linking the mesogen groups to the linking groups, thespacing groups being selected from the group consisting of poly(alkyleneoxide), polyalkane, polyperfluoroalkane, polysiloxane, and aliphaticpolyether.
 37. A waveplate according to claim 28 wherein the side chainsfurther comprise spacing groups linking the mesogen groups to thelinking groups, the spacing groups being selected from the groupconsisting of poly(alkylene oxide), polyalkane, polyperfluoroalkane,polysiloxane, and aliphatic polyether.
 38. A waveplate according toclaim 1 wherein the spacing groups are sufficiently long andsufficiently flexible to allow the mesogens of adjacent sidechains toassociate as a film of the mesogen-containing polymer is stretched. 39.A planar lightwave circuit comprising a waveguide and a waveplateaccording to any of claims 1, 2, 3, 7, 8, 10, 11, 12, 13, 18, 20, 24,26, and 29 positioned in an optical pathway of the waveguide.
 40. Aplanar lightwave circuit according to claim 39 wherein the waveguide isone of a plurality of waveguides of an arrayed waveguide gratingpositioned between two free propagation regions of the planar lightwavecircuit, and wherein the waveplate is positioned in an optical pathwayof each of the plurality of waveguides of the arrayed waveguide grating.41. A planar lightwave circuit according to claim 39 wherein thewaveplate is positioned at an angle to the waveguides that reduces backreflection caused by the waveplate groove, glue, and waveplate.
 42. Amethod of making an optical device comprising (a) providing amesogen-containing polymer film; and (b) forming the mesogen-containingpolymer piece to have a length, a width, and a thickness adapted for usein a planar lightwave circuit, the mesogen-containing polymer piecehaving a birefringence not equal to zero, said birefringence beingsuitable for use in a waveguide of a planar lightwave circuit
 43. Amethod according to claim 42 and further comprising inserting thepolymer piece into an optical pathway of a waveguide of the planarlightwave circuit.
 44. A method according to claim 42 wherein themesogen-containing polymer film has a polymer backbone selected from thegroup consisting of polyimides, polyetherimides, polyesterimides,polyamideimides, polyketones, polyarylethers, polyetherketones,polysulfones, polysulfides, polyarylenes, polyesters, polyamides,polycarbonates, polyolefins, polyvinylesters, polyurethanes,polyacrylates, polyphenylenes.
 45. A method according to claim 42wherein the mesogen-containing polymer film contains at least onemesogen having the form phenyl-X-phenyl-R or phenyl-phenyl-R, where X isselected from the group consisting of azo, diazo, azoxy, nitrone,carbon-carbon double bond, carbon-carbon triple bond, amide, imide,Schiff base, and ester; and R is selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 46. A method according to claim 42 wherein themesogen groups are selected from the group consisting of trans 1,3cyclohexane; trans 1,4 cyclohexane; trans 2,5 disubstituted 1,3 dioxane;trans 2,5 disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3dioxathiane.
 47. A method according to claim 44 wherein themesogen-containing polymer film contains at least one mesogen having theform phenyl-X-phenyl-R or phenyl-phenyl-R, where X is selected from thegroup consisting of azo, diazo, azoxy, nitrone, carbon-carbon doublebond, carbon-carbon triple bond, amide, imide, Schiff base, and ester;and R is selected from the group consisting of poly(alkylene oxide),polyalkane, polyperfluoroalkane, polysiloxane, and aliphatic polyether.48. A method according to claim 44 wherein the mesogen groups areselected from the group consisting of trans 1,3 cyclohexane; trans 1,4cyclohexane; trans 2,5 disubstituted 1,3 dioxane; trans 2,5disubstituted 1,3 dithiane; and trans 2,5 disubstituted 1,3 dioxathiane.49. A method according to claim 42 wherein the mesogen-containingpolymer film has at least one linking group selected from the groupconsisting of ether, ester, amide, imide, urethane, alkylene, alkyl. 50.A method according to claim 44 wherein the mesogen-containing polymerfilm has at least one linking group selected from the group consistingof ether, ester, amide, imide, urethane, alkylene, alkyl.
 51. A methodaccording to claim 45 wherein the mesogen-containing polymer film has atleast one linking group selected from the group consisting of ether,ester, amide, imide, urethane, alkylene, alkyl.
 52. A method accordingto claim 46 wherein the mesogen-containing polymer film has at least onelinking group selected from the group consisting of ether, ester, amide,imide, urethane, alkylene, alkyl.
 53. A method according to claim 47wherein the mesogen-containing polymer film has at least one linkinggroup selected from the group consisting of ether, ester, amide, imide,urethane, alkylene, alkyl.
 54. A method according to claim 48 whereinthe mesogen-containing polymer film has at least one linking groupselected from the group consisting of ether, ester, amide, imide,urethane, alkylene, alkyl.
 55. A method according to claim 42 whereinthe mesogen-containing polymer film has at least one spacer groupselected from the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 56. A methodaccording to claim 44 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 57. A method according to claim 45 wherein themesogen-containing polymer film has at least one spacer group selectedfrom the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 58. A methodaccording to claim 46 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 59. A method according to claim 47 wherein themesogen-containing polymer film has at least one spacer group selectedfrom the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 60. A methodaccording to claim 48 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 61. A method according to claim 49 wherein themesogen-containing polymer film has at least one spacer group selectedfrom the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 62. A methodaccording to claim 50 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 63. A method according to claim 51 wherein themesogen-containing polymer film has at least one spacer group selectedfrom the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 64. A methodaccording to claim 52 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 65. A method according to claim 53 wherein themesogen-containing polymer film has at least one spacer group selectedfrom the group consisting of poly(alkylene oxide), polyalkane,polyperfluoroalkane, polysiloxane, and aliphatic polyether.
 66. A methodaccording to claim 54 wherein the mesogen-containing polymer film has atleast one spacer group selected from the group consisting ofpoly(alkylene oxide), polyalkane, polyperfluoroalkane, polysiloxane, andaliphatic polyether.
 67. A method of using a mesogen-containing polymer,said method comprising processing the mesogen-containing polymer into afilm with birefringence in the plane of the film, inserting themesogen-containing polymer film into an optical pathway of a waveguideof a planar lightwave circuit such that the polymer effects a change inan optical signal transmitted through the waveguide and the polymer. 68.A method of using a mesogen-containing polymer comprising passing anoptical signal having a first polarization state through a waveguide andthe polymer such that the optical signal has a second polarization statenot identical to the first polarization state.